Littérature scientifique sur le sujet « DISCREATE CASINE TRANSFORM »
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Articles de revues sur le sujet "DISCREATE CASINE TRANSFORM"
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Cai, Jian Cheng, Yong Hai Zhang et Shuang Li Long. « Computational Estimation of Fan Casing Noise at Blade Passing Frequency Component Noise ». Applied Mechanics and Materials 184-185 (juin 2012) : 95–100. http://dx.doi.org/10.4028/www.scientific.net/amm.184-185.95.
Texte intégralRésumé :
This paper studies both vibroacoustics and aeroacoustics of a centrifugal fan casing; the aim of this study is to explore a methodology to make quantitative predictions of fan casing noise. The spectra of the fan noise and casing vibration were firstly presented; discrete components related to the rotational frequency protrude in the spectra, especially the blade passing frequency (BPF). Computational fluid dynamics (CFD) technique was used to obtain the three-dimensional unsteady turbulent internal flow. Attention was paid to the pressure fluctuations on the volute wall; the shapes of pressure fluctuation were nearly sinusoidal in nature, with the BPF as the primary frequency. On the vibroacoustic side, Fast Fourier Transform (FFT) was applied to the time series of pressure fluctuations to extract the BPF component. A finite element analysis (FEA) model of the casing structure was constructed, and was validated by experimental modal analysis. The harmonic dynamic response of the casing structure was calculated with the BPF pressure fluctuation component as the excitation. The vibration results were then taken as the velocity (Neumann) boundary condition for the noise radiation model which was built in boundary element method (BEM), and the sound radiation was calculated. On the aeroacoustic side, the BPF component of pressure fluctuations was modeled as acoustic dipole source, and sound radiation was also solved by BEM. Results show that the sound pressure level (SPL) of vibroacoustics is fairly small compared to the aeroacoustic counterpart. This study shows that CFD, FEA together with BEM can be used to numerically predict BPF casing noise of turbomachinery successfully.
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Chen, Jianyou, Junrui Ning, Wenchao Chen, Xiaokai Wang, Wei Wang et Gulan Zhang. « Distributed acoustic sensing coupling noise removal based on sparse optimization ». Interpretation 7, no 2 (1 mai 2019) : T373—T382. http://dx.doi.org/10.1190/int-2018-0080.1.
Texte intégralRésumé :
The industry treats the distributed acoustic sensing (DAS) system, which uses an optical fiber cable in vertical seismic profiling (VSP) data acquisition, as a new and fast-growing technology. The high-quality data set acquired from the DAS acquisition system can produce high-precision VSP images and obtain more detailed checkshots. However, in field data, the acquired VSP data set suffers from strong coherent DAS coupling noise. Many factors may cause coherent DAS coupling noise, such as the cable slapping and ringing due to the physical placement, the regular swing of the wireline in the well, and the uncoupling between the fiber cable and the casing. This DAS coupling noise reduces the signal-to-noise ratio and affects the subsequent processing and interpretation. Removing the DAS coupling noise can help to improve the quality of the VSP data set acquired with the DAS system. We have developed a sparse-optimization-based DAS coupling noise removing method. In the DAS-based VSP data set, the effective signal and the coupling noise have distinct morphological characteristics. The effective VSP signal has a wide bandwidth, whereas the DAS coupling noise appears in some narrow frequency bands in the frequency domain. The continuous wavelet transform and the discrete cosine transform can sparsely represent the effective VSP signal and DAS coupling noise, respectively. Therefore, we choose these two transforms as two sparse dictionaries and combine them to form an overcomplete dictionary. The morphological component analysis (MCA) can use the morphological difference between different components and the overcomplete dictionary to sparsely represent all components in the complicated signal. Based on the MCA theory, we use the block coordinate relaxation algorithm to separate the effective VSP signal and DAS coupling noise. Applications on a synthetic data set and two field data sets have validated the effectiveness of our method.
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Hendry, Jans, Isnan Nur Rifai et Yoga Mileniandi. « Sampled and discretized of short-time Fourier transform and non-negative matrix factorization : the single-channel source separation case ». Jurnal Teknologi dan Sistem Komputer 9, no 1 (27 novembre 2020) : 41–48. http://dx.doi.org/10.14710/jtsiskom.2020.13858.
Texte intégralRésumé :
The Short-time Fourier transform (STFT) is a popular time-frequency representation in many source separation problems. In this work, the sampled and discretized version of Discrete Gabor Transform (DGT) is proposed to replace STFT within the single-channel source separation problem of the Non-negative Matrix Factorization (NMF) framework. The result shows that NMF-DGT is better than NMF-STFT according to Signal-to-Interference Ratio (SIR), Signal-to-Artifact Ratio (SAR), and Signal-to-Distortion Ratio (SDR). In the supervised scheme, NMF-DGT has a SIR of 18.60 dB compared to 16.24 dB in NMF-STFT, SAR of 13.77 dB to 13.69 dB, and SDR of 12.45 dB to 11.16 dB. In the unsupervised scheme, NMF-DGT has a SIR of 0.40 dB compared to 0.27 dB by NMF-STFT, SAR of -10.21 dB to -10.36 dB, and SDR of -15.01 dB to -15.23 dB.
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J, Prawin. « Bearing Fault Diagnosis usingEnhanced Envelope Analysis ». e-Journal of Nondestructive Testing 27, no 11 (novembre 2022). http://dx.doi.org/10.58286/27472.
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Early fault detection and diagnosis of bearing is of paramount importance in wind turbines as it contributes to around 70% of gearbox and 21%-70% of generator failure. This paper presents an enhanced envelope analysis technique for bearing fault identification using vibration measurements. The raw vibration signal measured from the outer casing of the WT gearbox with faulty bearing has not only fault frequency component but also resonant frequency, discrete frequency (gear and shaft) and high frequency background noise. The present work diagnose bearing faults through a three-step process: i) using Auto- Regressive(AR) time series model to remove discrete frequency components of gear and shaft ii) fault-sensitive frequency and demodulation band selection using spectral kurtosis. The spectral kurtosis is expected to higher around the region of resonance frequencies when fault occurs otherwise the fault signal is modulated. iii) envelope analysis to obtain spectrum by Hilbert Transform (HT) and retrieval of fault information. The order of the AR model is chosen such that the residual signal exhibits maximum kurtosis and spectral kurtosis is computed through short time Fourier Transform (STFT). The enhanced envelope analysis technique for bearing fault diagnosis is verified and validated using numerical simulations and Korea Aerospace University bearing damage benchmark datasets.
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Wang, Ting, et Reda Ragab. « Investigation of Applicability of Transporting Water Mist for Cooling Turbine Blades ». Journal of Thermal Science and Engineering Applications 12, no 1 (7 septembre 2019). http://dx.doi.org/10.1115/1.4042860.
Texte intégralRésumé :
Abstract This paper presents a numerical study to investigate the feasibility of transporting water mist to the rotating blades of a high-pressure turbine. The idea of using mist film cooling to enhance conventional air cooling has been proven to be a feasible technique under laboratory conditions. However, there are challenges in implementing this scheme for real gas turbine systems. The first challenge is how to transport the mist to the rotating blades and the second challenge is delivering the mist to the injection holes and getting the particles to survive within the harsh gas turbine environment. Both a zero-dimensional mist evaporation analytical model and a 3D computational fluid dynamics (CFD) scheme are employed for analysis. In the CFD simulation, the Lagrangian–Eulerian method is used along with the discrete phase model (DPM) to track the evaporation process of each individual water droplet. For transporting the mist to the blades, the high-pressure water mist is injected into the stream of cooling air extracted from the compressor through two different passages. The first passage passes through the rotor cover-plate cavity before entering the blade base. The second passage passes through a diaphragm box on the base of the second vane, then tangentially through a cooling passage in the rotating shaft, and eventually to the blade base. The results show that it is feasible to transport the mist from the turbine casing to the blade through both passages, provided that droplets with sufficient particle diameter and mist loading are used. The shorter passage, through the nozzle diaphragm, alleviates a lot of challenges facing the passage through the blade cavity and seems to be more practical. A side benefit of transporting mist through the internal passages is the additional cooling of the preswirler and rotor cover plates. The results are encouraging for implementing the mist cooling technique under real gas turbine conditions.
Thèses sur le sujet "DISCREATE CASINE TRANSFORM"
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YADAV, PRASHIT. « DETECTION OF COPY MORE FORGERY IN DIGITAL IMAGES USING AN OPTIMIZED BLOCK BASED APPROACH ». Thesis, 2016. http://dspace.dtu.ac.in:8080/jspui/handle/repository/14922.
Texte intégralRésumé :
Technology is growing exponentially and so does the sophistication of various imaging tools
that makes it easier for a person to forge digital images. There are several types of forgeries
which are done on images out of which Copy-Move is one of the most widely used. In this
type of forgery a portion of an image is copied and pasted over to another portion to conceal
some information. Several approaches have been developed so far to detect such kind of
forgery. In the block based approach the image is divided into overlapping blocks and each
block is matched against every other block for similarity. However such a matching would be
computationally expensive, thus each block’s dimensionality is reduced by extracting its vital
features and using this information for representation of the block. To extract the features we
first applied the Laplacian of Gaussian filter on the image to highlight the areas of interest
such as edges, blobs, etc. Subsequently we used Discrete Cosine Transform algorithm on
each block to generate DCT coefficient matrix for each block. The DCT coefficients matrix is
quantized and averaging is used to extract a feature set with reduce dimensionality. Now
these feature vectors with respect to each block are stored in a matrix called feature vector
matrix. The matrix is then lexicographically sorted so that vectors corresponding to similar
blocks come adjacent to each other. The decision of forgery can then be taken if a number of
connected/similar blocks are equidistant to each other. The feature extraction is vital as not
only does it reduce the computation complexity but choosing the correct set of features makes
an approach invariant to various image manipulations such as rotation, translation, scaling,etc.
Livres sur le sujet "DISCREATE CASINE TRANSFORM"
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Walsh, Bruce, et Michael Lynch. Short-term Changes in the Mean : 2. Truncation and Threshold Selection. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198830870.003.0014.
Texte intégralRésumé :
The selection intensity, the mean change in a trait within a generation expressed in phenotypic standard deviations, provides an important metric for comparing the strength of selection over designs. Further, under truncation selection (only individuals above some threshold leave offspring), the selection intensity is a function of the fraction saved, and hence the breeder's equation is often expressed in terms of the selection intensity. An important special case of truncation selection is a threshold trait, wherein an individual only expresses a particular phenotype when its underlying liability value exceeds some threshold. This chapter examines selection on such traits, and generalizes this binary-trait setting (with binomial residuals) to other classes of discrete traits, wherein some underling linear model (generating the threshold) is this transformed via a generalized linear mixed model into an observed trait value.
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Searle, Alison. Exiles at Home. Sous la direction de Andrew Hiscock et Helen Wilcox. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780199672806.013.25.
Texte intégralRésumé :
The radical and repeated changes in state religion, accompanied by persecution of any who openly dissented from the status quo, meant that there were numerous groups who found themselves in exile at home in England during the sixteenth and seventeenth centuries. This chapter focuses on the experience of Protestant Nonconformists in the later seventeenth century. It examines the ways in which Nonconformist communities interpreted their experiences, interrogating and recording these in a variety of literary genres. The concept of exile at home is analysed through five discrete and interconnected categories: imprisonment; legal disputation in the courts; corporate worship; itinerant preaching; and letter writing. Each section draws upon a number of case studies that illustrate the wide range of spiritual experiences and theological convictions in Nonconformist communities and how these were encapsulated, transformed, and disputed in journals, letters, sermons, and biographies, amongst other literary genres.
Chapitres de livres sur le sujet "DISCREATE CASINE TRANSFORM"
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Jawaid, A., et J. Seewig. « Discrete Filter and Non-Gaussian Noise for Fast Roughness Simulations with Gaussian Processes ». Dans Proceedings of the 3rd Conference on Physical Modeling for Virtual Manufacturing Systems and Processes, 1–15. Cham : Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-35779-4_1.
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AbstractRough surface simulations result in tight feedback loops in research procedures, such that they speed up studies for example about roughness’ impact on tribology or fluid dynamics. To model and simulate a broad spectrum of rough surfaces, Gaussian processes (GP) have been suggested recently. However, these models are limited on surfaces with small sizes since computational time-costs and memory-costs of simulations with standard procedures scale cubically and quadratically, respectively. In this paper, we apply the discrete filter approach which is a special case of GPs. We use the discrete filter with the fast Fourier transform (FFT) algorithm to efficiently sample from a high-dimensional Gaussian distribution and we compare its computational costs with the contour integral quadrature algorithm. Our experiments show that GPs benefit from FFT and allow stationary rough surfaces with sizes as large as 30, 000 × 30, 000 to be efficiently sampled. Since this approach is complementary to the GP and noise model approach, we also show simulations of rough surfaces with underlying non-Gaussian noise models that can reduce computational complexity.
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Ionescu, Alexandru D., Akos Magyar et Stephen Wainger. « Averages along Polynomial Sequences in Discrete Nilpotent Lie Groups : Singular Radon Transforms ». Dans Advances in Analysis, sous la direction de Charles Fefferman, Alexandru D. Ionescu, D. H. Phong et Stephen Wainger. Princeton University Press, 2014. http://dx.doi.org/10.23943/princeton/9780691159416.003.0007.
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This chapter concentrates on the averages of functions along polynomial sequences in discrete nilpotent groups, illustrating the problems that arise from studying these averages. Though special polynomial sequences can still use the Fourier transform in the central variables to analyze the operators, it appears that one needs to proceed in an entirely different way in the case of general polynomial maps, when the Fourier transform method is not available. This chapter is the first attempt to treat discrete Radon transforms along general polynomial sequences in the non-commutative nilpotent settings. It does so by analyzing the problem of L² boundedness of singular Radon transforms.
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Bulnes, Francisco. « A Modern Review of Wavelet Transform in Its Spectral Analysis ». Dans Recent Advances of Wavelet Transform and Their Applications [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.105559.
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The spectral analysis, in much aspects as are the wavelet transform in its numerous versions and its relation with other transforms and special functions requires a special review, since the exploration in the frequency domain to the wavelet transform is more detailed and majorly more specific in different applications. For example, the wavelet transform of special function can be very useful to create and design special signal filters or, for example, to the interphase between reception-emission devices with sensorial parts of the human body. Also the quantum wavelet transform is very useful in the spectral study of traces of particles. Likewise, in this chapter, these aspects are considered as an inherent property of the wavelet transform in the spectral exploration of some phenomena. Finally, general results to the discrete case are given, which is analyzed to the wavelet transform and its spectra.
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Alegeh, Nurudeen, Munavar Thottoli, Naeem Mian, Andrew Longstaff et Simon Fletcher. « Feature Extraction of Time-Series Data Using DWT and FFT for Ballscrew Condition Monitoring ». Dans Advances in Transdisciplinary Engineering. IOS Press, 2021. http://dx.doi.org/10.3233/atde210069.
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This paper investigates the use of the discrete wavelet transform (DWT) and Fast Fourier Transform (FFT) to improve the quality of extracted features for machine learning. The case study in this paper is detecting the health state of the ballscrew of a gantry type machine tool. For the implementation of the algorithm for feature extraction, wavelet is first applied to the data, followed by FFT and then useful features are extracted from the resultant signal. The extracted features were then used in various machine learning algorithms like decision tree, K-nearest neighbour (KNN) and support vector machine (SVM) for binary classification of the ballscrew state. The result shows significant improvement in the classification accuracy after the wavelet transform and FFT has been performed on the data.
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West-Eberhard, Mary Jane. « Cross-sexual Transfer ». Dans Developmental Plasticity and Evolution. Oxford University Press, 2003. http://dx.doi.org/10.1093/oso/9780195122343.003.0021.
Texte intégralRésumé :
Distinctive male and female traits are perhaps the most familiar of all divergent specializations within species. In cross-sexual transfer, discrete traits that are expressed exclusively in one sex in an ancestral species appear in the opposite sex of descendants. An example is the expression of brood care by males in a lineage where ancestral females are the exclusive caretakers of the young, as in some voles (Thomas and Birney, 1979). Despite the prominence of sexual dimorphism and sex reversals in nature, and an early explicit treatment by Darwin, discussed in the next section, cross-sexual transfer is not often recognized as a major factor in the evolution of novelty (but see, on animals, Mayr, 1963, pp. 435-439; Mayr, 1970, p. 254; on plants, Iltis, 1983). When more widely investigated, cross-sexual transfer may prove to rival heterochrony and duplication as an important source of novelties in sexually dimorphic lineages. For this reason, I devote more attention here to cross-sexual transfer than to these other, well-established general patterns of change. The male and female of a sexually dimorphic species may be so different that it is easy to forget that each individual carries most or all of the genes necessary to produce the phenotype of the opposite sex. Sex determination, like caste determination and other switches between alternative phenotypes, depends on only a few genetic loci or, in many species, environmental factors (Bull, 1983). There is considerable flexibility in sex determination and facultative reversal in some taxa. Among fish, for example, there is even a species wherein sex is determined by juvenile size at a critical age (Francis and Barlow, 1993). The sex determination mechanism, whatever its nature, leads to a series of sex-limited responses, often coordinated by hormones and not necessarily all occurring at once. A distinguishing aspect of sexually dimorphic traits in adults is that there is often a close homology between the secondary sexual traits that are differently modified in the two sexes.
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El-said, Shaimaa A., Khalid F. A. Hussein et Mohamed M. Fouad. « Image Compression Technique for Low Bit Rate Transmission ». Dans Intelligent Computer Vision and Image Processing, 211–29. IGI Global, 2013. http://dx.doi.org/10.4018/978-1-4666-3906-5.ch015.
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A novel Adaptive Lossy Image Compression (ALIC) technique is proposed to achieve high compression ratio by reducing the number of source symbols through the application of an efficient technique. The proposed algorithm is based on processing the discrete cosine transform (DCT) of the image to extract the highest energy coefficients in addition to applying one of the novel quantization schemes proposed in the present work. This method is straightforward and simple. It does not need complicated calculation; therefore the hardware implementation is easy to attach. Experimental comparisons are carried out to compare the performance of the proposed technique with those of other standard techniques such as the JPEG. The experimental results show that the proposed compression technique achieves high compression ratio with higher peak signal to noise ratio than that of JPEG at low bit rate without the visual degradation that appears in case of JPEG.
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Mejia, Rodolfo Villamizar, Jhonatan Camacho Navarro et Wilmer Alexis Sandoval Caceres. « Case-Based Reasoning for Stiffness Changes Detection in Structures ». Dans Emerging Design Solutions in Structural Health Monitoring Systems, 124–52. IGI Global, 2015. http://dx.doi.org/10.4018/978-1-4666-8490-4.ch007.
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This chapter presents an expert monitoring algorithm approach to detect, locate and quantify stiffness variations in structures. The algorithm is based on pattern recognition and artificial intelligence techniques that emulate knowledge based on human reasoning. The expert system (ES) uses time-frequency information about dynamics of structure, which is processed by using discrete wavelet transform (DWT), self-organizing maps (SOM), case-based reasoning (CBR) and principal component analysis (PCA). In addition, two applications are considered in order to evaluate the effectiveness of vibration analysis methodology and CBR in damage detection. The first application (Camacho 2010) uses the environmental excitation to detect and quantify damage in a Mechanical UBC ASCE Benchmark. The second one (Sandoval 2010) uses a predesigned signal to detect geometric damages on a gas pipeline. In both cases, a finite element model (FEM) is used to simulate different damages scenarios, which correspond to stiffness variations in different location.
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Prasada Rao Borra, Surya, Kongara Ramanjaneyulu et K. Raja Rajeswari. « A Robust and Oblivious Watermarking Method Using Maximum Wavelet Coefficient Modulation and Genetic Algorithm ». Dans Modeling and Simulation in Engineering - Selected Problems. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.93832.
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An image watermarking method using Discrete Wavelet Transform (DWT) and Genetic Algorithm (GA) is presented for applications like content authentication and copyright protection. This method is robust to various image attacks. For watermark detection/extraction, the cover image is not essential. Gray scale images of size 512 × 512 as cover image and binary images of size 64 × 64 as watermark are used in the simulation of the proposed method. Watermark embedding is done in the DWT domain. 3rd and 2nd level detail sub-band coefficients are selected for further processing. Selected coefficients are arranged in different blocks. The size of the block and the number blocks depends on the size of the watermark. One watermark bit is embedded in each block. Then, inverse DWT operation is performed to get the required watermarked image. This watermarked image is used for transmission and distribution purposes. In case of any dispute over the ownership, the hidden watermark is decoded to solve the problem. Threshold-based method is used for watermark extraction. Control parameters are identified and optimized based on GA for targeted performance in terms of PSNR and NCC. Performance comparison is done with the existing works and substantial improvement is witnessed.
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Aswini, K. R. N., et S. Vijayaraghavan. « Denoising of Ultrasonic B – Scan Retinal Images for ealier Detection of Retinopathy of Prematurity (RoP) ». Dans New Frontiers in Communication and Intelligent Systems, 661–70. Soft Computing Research Society, 2021. http://dx.doi.org/10.52458/978-81-95502-00-4-67.
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Human eye is a complex mechanism that enables us the sense of vision. Retina, being one of the most important layers of eye, in any case gets affected, leads to severe visual impairment and sometimes loss of vision too. Retinopathy of Prematurity (RoP), being a by birth condition in untimely children? wherein an anomaly is available in the retinal layers and the related veins. Ultrasonic B – Scan is the prominent diagnostic tool used to identify RoP. Effective, Early and Simplified diagnostic and imaging tools aid the Ophthalmologists for an accurate diagnosis and work towards the prevention of vision loss. In this paper, RoP images of Oculus Dextrusand Ocular Sinister – Left eye in severe stage are considered for filtering and noise removal. Wavelet denoising of B-scan images is performed through Discrete Wavelet Transform (DWT) and with different thresholding such as Global thresholding. Then, the location of prematurity in retina is found out, in comparison with the healthy retina. An optimum thresholding level is fixed, which is followed by the calculation of statistical mean, variance and standard deviation. This model helps to find out the abnormality of retina, the location and severity in mathematical terms. The denoising of the distorted images is found to be potential enough in achieving the effective diagnosis in the case of RoP in children.
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Yury, Yanilkin, Shmelev Vladimir et Kolobyanin Vadim. « A Monotonic Method of Split Particles ». Dans Recent Advances on Numerical Simulations [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.97044.
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The problem of correct calculation of the motion of a multicomponent (multimaterial) medium is the most serious problem for Lagrangian–Eulerian and Eulerian techniques, especially in multicomponent cells in the vicinity of interfaces. There are two main approaches to solving the advection equation for a multicomponent medium. The first approach is based on the identification of interfaces and determining their position at each time step by the concentration field. In this case, the interface can be explicitly distinguished or reconstructed by the concentration field. The latter algorithm is the basis of widely used methods such as VOF. The second approach involves the use of the particle or marker method. In this case, the material fluxes of substances are determined by the particles with which certain masses of substances bind. Both approaches have their own advantages and drawbacks. The advantages of the particle method consist in the Lagrangian representation of particles and the possibility of” drawbacks. The main disadvantage of the particle method is the strong non-monotonicity of the solution caused by the discrete transfer of mass and mass-related quantities from cell to cell. This paper describes a particle method that is free of this drawback. Monotonization of the particle method is performed by spliting the particles so that the volume of matter flowing out of the cell corresponds to the volume calculated according to standard schemes of Lagrangian–Eulerian and Eulerian methods. In order not to generate an infinite chain of spliting, further split particles are re-united when certain conditions are met. The method is developed for modeling 2D and 3D gas-dynamic flows with accompanying processes, in which it is necessary to preserve the history of the process at Lagrangian points.
Actes de conférences sur le sujet "DISCREATE CASINE TRANSFORM"
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Espiritu Santo, A., et C. Carbajal. « Respiration rate extraction from ECG signal via discrete wavelet transform ». Dans 2010 2nd Circuits and Systems for Medical and Environmental Applications Workshop (CASME). IEEE, 2010. http://dx.doi.org/10.1109/casme.2010.5706679.
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Sun, Zixiang, Nicholas J. Hills et Richard Scott. « A CFD Assessment of Engine Core Zone Casing Heat Transfer ». Dans ASME Turbo Expo 2019 : Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-90381.
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Abstract A systematic CFD investigation was conducted to assess the core zone (CZ) casing heat transfer of a large civil aircraft engine. Three key engine operating conditions, maximum takeoff (MTO), cruise (CRZ) and ground idle (GI) were analyzed. Steady flows were assumed. Turbulence was simulated using the realizable k-epsilon model in conjunction with the scalable wall function. Buoyancy effect was taken into account. Radiation was calculated using the discrete ordinate (DO) model. It was shown that the forced convection heat transfer dominates in most of the casing surface in the core zone, and radiation is of second importance in general. However, in some areas where both convection and radiation heat transfer are weak but the latter is relatively greater in magnitude than the former, radiation heat transfer could thus become dominant. In addition, the overall impact of radiation on casing heat transfer increases from MTO to CRZ and GI conditions, as the strength of engine load decreases. The overall effect of buoyancy on casing heat transfer is small, but could be noticeable in some local areas where flow velocity is low. The insight into heat transfer features on the engine core zone casing supported by quantified CFD evidences is the first in the public domain, as far as authors are aware.
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Cuadrado, David G., Francisco Lozano, Valeria Andreoli et Guillermo Paniagua. « Engine-Scalable Rotor Casing Convective Heat Flux Evaluation Using Inverse Heat Transfer Methods ». Dans ASME Turbo Expo 2018 : Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-76906.
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In this paper, we propose a two-step methodology to evaluate the convective heat flux along the rotor casing using an engine-scalable approach based on Discrete Green’s Functions. The first step consists in the use of an inverse heat transfer technique to retrieve the heat flux distribution on the shroud inner wall by measuring the temperature of the outside wall; the second step is the calculation of the convective heat flux at engine conditions, using the experimental heat flux and the Green Functions engine-scalable technique. Inverse methodologies allow the determination of boundary conditions, in this case the inner casing surface heat flux, based on measurements from outside of the system, which prevents aerothermal distortion caused by routing the instrumentation into the test article. The heat flux, retrieved from the inverse heat transfer methodology, is related to the rotor tip gap. Therefore, for a given geometry and tip gap, the pressure and temperature can also be retrieved. In this work, the Digital Filter Method is applied in order to take advantage of the response of the temperature to heat flux pulses. The Discrete Green’s Function approach employs a matrix to relate an arbitrary temperature distribution to a series of pulses of heat flux. In the present procedure, the terms of the Green’s Function matrix are evaluated with the output of the inverse heat transfer method. Given that key dimensionless numbers are conserved, the Green’s Functions matrix can be extrapolated to engine-like conditions. A validation of the methodology is performed by imposing different arbitrary heat flux distributions, to finally demonstrate the scalability of the Green’s Function Method to engine conditions. A detailed uncertainty analysis of the two-step routine is included based on the value of the pulse of heat flux, the temperature measurement uncertainty, the thermal properties of the material and the physical properties of the rotor casing.
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Jaafar, Abdul A., Fariborz Motallebi, Michael Wilson et J. Michael Owen. « Flow and Heat Transfer in a Rotating Cavity With a Stationary Stepped Casing ». Dans ASME Turbo Expo 2000 : Power for Land, Sea, and Air. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/2000-gt-0281.
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In this paper, new experimental results are presented for the flow in a co-rotating disc system with a rotating inner cylinder and a stationary stepped outer casing. The configuration is based on a turbine disc-cooling system used in a gas turbine engine. One of the rotating discs can be heated, and cooling air is introduced through discrete holes angled inward at the periphery of this disc. The cooling air leaves the system through axial clearances between the discs and the outer casing. Some features of computed flows, and both measured and computed heat transfer, were reported previously for this system. New velocity measurements, obtained using Laser Doppler Anemometry, are compared with results from axisymmetric, steady, turbulent flow computations obtained using a low-Reynolds-number k-ε turbulence model. The measurements and computations show that the tangential component of velocity is invariant with axial location in much of the cavity, and the data suggest that Rankine (combined free and forced) vortex flow occurs. The computations fail to reproduce this behaviour, and there are differences between measured and computed details of secondary flow recirculations. Possible reasons for these discrepancies, and their importance for the prediction of associated heat transfer, are discussed.
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Lynch, J., C. G. Durfee et H. M. Milchberg. « Leaky Mode Propagation in a High Intensity Plasma Waveguide ». Dans High Resolution Fourier Transform Spectroscopy. Washington, D.C. : Optica Publishing Group, 1994. http://dx.doi.org/10.1364/hrfts.1994.wc5.
Texte intégralRésumé :
The finite thickness of the electron density barrier in the shock driven plasma waveguide1 (see Fig. 1 of paper Mode Properties of a High Intensity Plasma Waveguide, this conference) implies that formally, there are no bound modes (ie. no discrete spectrum of channel propagation wavenumbers) since all fields leak to some extent. For sufficiently large ΔNe and rm (where ΔNe = Ne(rm)-Ne(0) is the electron density difference between the peak and on-axis electron density and rm is the radius to the electron density peak), low order leaky waveforms are effectively indistinguishable from eigenmodes of a channel having Ne(r)= Nemax for r>rm (idealized channel). As an example of this, Fig. 1 compares leaky waveforms from a model channel (consistent with predictions of our laser-plasma hydrodynamics code1) to eigenmodes of the corresponding idealized channel. In this case, the field attenuation in the walls is sufficient to result in little tunneling or leakage of the lowest order p=0, m=0 mode (where p and m are radial and azimuthal mode indices). The p=1, m=0 mode, however, is sensitive to the finite barrier thickness in this case.
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Lu, Xiaodong, et Pei-Feng Hsu. « Parallel Computing of Two Numerical Quadratures for an Integral Formulation of Transient Radiation Transport ». Dans ASME 2003 Heat Transfer Summer Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/ht2003-47235.
Texte intégralRésumé :
Parallel computing of the transient radiative transfer process in the three-dimensional homogeneous and nonhomogeneous participating media is studied with an integral equation model. The model can be used for analyzing the ultra-short light pulse propagation within the highly scattering media. Two numerical quadratures are used: the discrete rectangular volume (DRV) method and YIX method. The parallel versions of both methods are developed for one-dimensional and three-dimensional geometries, respectively. Both quadratures achieve good speedup in parallel performance. Because the integral equation model uses very small amount of memory, the parallel computing can take advantage of having each compute node or processor store the full spatial domain information without using the typical domain decomposition parallelism, which will be necessary in other solution methods, e.g., discrete ordinates and finite volume methods, for large scale simulations. The parallel computation is conducted by assigning different portion of the quadrature to different compute node. In DRV method, a variation of the spatial domain decomposition is used. In the case of YIX scheme, the angular quadrature is divided up according to the number of compute nodes, instead of the spatial domain being divided. This parallel scheme minimizes the communications overhead. The only communication needed is at the end of each time step when each node shares the partial integrated result of the current time step with all other compute nodes. The angular quadrature decomposition approach leads to very good parallel efficiency. Two new discrete ordinate sets are used in the YIX angular quadrature and their parallel performances are discussed. One of the discrete ordinates sets, called spherical ring set, is also suitable for use in the conventional discrete ordinates method.
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Panta Pazos, Rube´n. « Treatment of Noise in Experimental Transport Measurements Plots With Discrete Wavelet Transforms ». Dans 17th International Conference on Nuclear Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/icone17-75731.
Texte intégralRésumé :
In this work it is applied the wavelet transform method [2] in order to reduce diverse type of noises of experimental measurement plots in transport theory. First, suppose that a problem is governed by the transport equation for neutral particles, and an unknown perturbation occurs. In this case, the perturbation can be associated to the source, or even to the flux inside the domain X. How is the behavior of the perturbed flux in relation to the flux without the perturbation? For that, we employ the wavelet transform method in order to compress the angular flux considered as a 1D, or n-th dimensional signal ψ. The compression of this signal can be performed up to some a convenient order (that depends of the length of the signal). Now, the transport signal is decomposed as [9, 11]: ψ=〈am|dm|dm−1|dm−2|⋯|d2|d1〉 where ak represents the sub signal of k-th level generated by the low-pass filter associated to the discrete wavelet transform (DWT) chosen, and dk the sub signal of k-th level generated by the high-pass filter associated to the same DWT. It is applied basically the Haar, Daub4 and Coiflet wavelets transforms. Indeed, the sub signal am cumulates the energy, for this work of order 96% of the original signal ψ. A thresholding algorithm provides treatment for the noise, with significant reduction in the compressed signal. Then, it is established a comparison with a base of data in order to identify the perturbed signal. After the identification, it is recomposed the signal applying the inverse DWT. Many assumptions can be established: the rate signal-to-noise is properly high, the base of data must contain so many perturbed signals all with the same level of compression. The problem considered is for perturbations in the signal. For measurements the problem is similar, but in this case the unknown perturbations are generated by the apparatus of measurements, problems in experimental techniques, or simply by random noises. With the same above assumptions, the DWT is applied. For the identification, it is used a method evolving statistical and metric techniques. It is given some results obtained with an algebraic computer system.
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Trivedi, Ashish, Soumyadipta Basu et Kunal Mitra. « Transient Discrete Ordinate Method and Experiments of Pulsed Radiative Transfer Through Scattering Absorbing Media ». Dans ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56558.
Texte intégralRésumé :
The objective of this paper is to validate the solution of transient radiation transfer equation with experimental measurements using short pulse laser source having a Gaussian distribution. The transient radiative transfer equation for the case of short pulse laser propagation through scattering absorbing media such as tissue is an integrodifferential equation and is therefore complicated to solve. The time-dependent discrete ordinates method in conjunction with high order upwind piecewise parabolic interpolation scheme is used to solve the transient radiative transfer equation for the case of anisotropically scattering absorbing medium having a rectangular geometry in which an inhomogeneity is embedded. A parametric study involving different scattering and absorption coefficients of the medium, inhomogeneity and inhomogeneity size as well as the detector position is performed. The numerical modeling results and experimental measurements are in excellent agreement for various parameters studied in this paper.
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Kobayashi, M., S. Saito et S. Yamauchi. « Nonlinear Steady-State Rotordynamic Analysis Using Transfer Coefficient Method ». Dans ASME 1991 Design Technical Conferences. American Society of Mechanical Engineers, 1991. http://dx.doi.org/10.1115/detc1991-0228.
Texte intégralRésumé :
Abstract This paper proposes a new method for steady-state, large-order nonlinear rotordynamic calculations: it uses a method called the transfer coefficient method (TCM), which is more convenient than the transfer matrix method. Since TCM calls for only the displacement as the independent variable, whereas both the displacement and the force are needed as the state variables in the conventional transfer matrix method, TCM promises a substantial saving of computation time without incurring loss in the accuracy of calculation. First, the outline of TCM is explained, then the nonlinear calculations for a rotor of many degrees of freedom are presented. This steady-state nonlinear calculation method is based on the discreet Fourier transform (DPT, FFT) and substructure synthesis. As an example, the nonlinear response due to unbalance mass is calculated and discussed in the case of the rotor which is supported by three bearings with two nonlinear squeeze film dampers.
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Kuga, Yasuo, Akira Ishimaru, Hung-Wen Chang et Leung Tsang. « Comparisons between the small-angle approximation and the numerical solution for radiative transfer theory ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1986. http://dx.doi.org/10.1364/oam.1986.fl3.
Texte intégralRésumé :
The small-angle approximation for the radiative transfer theory is based on the assumption that the scattered wave is confined within a small angle in the forward direction. This assumption is generally valid for the turbulence case in which the turbulence size is much greater than the wavelength and the index of refraction is close to 1. However, the validity of this assumption for a discrete random medium with an index of refraction much greater than the surrounding medium is not well known. In spite of this, the small-angle approximation has sometimes been used for discrete random media because of its mathematical simplicity.