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Artykuły w czasopismach na temat "Circular separation dimension"
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Loeb, Sarah J., i Douglas B. West. "Fractional and circular separation dimension of graphs". European Journal of Combinatorics 69 (marzec 2018): 19–35. http://dx.doi.org/10.1016/j.ejc.2017.09.001.
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Liou, J. L., i J. F. Lin. "A Microcontact Model Developed for Asperity Heights with a Variable Profile Fractal Dimension, A Surface Fractal Dimension, Topothesy, and Non-Gaussian Distribution". Journal of Mechanics 25, nr 1 (marzec 2009): 103–15. http://dx.doi.org/10.1017/s1727719100003646.
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AbstractThe cross sections formed by the contact asperities of two rough surfaces at an interference are islandshaped, rather than having the commonly assumed circular contour. These island-shaped contact surface contours show fractal behavior with a profile fractal dimension Ds. The surface fractal dimension for the asperity heights is defined as D and the topothesy is defined as G. In the study of Mandelbrot, the relationship between D and Ds was given as D = Ds + 1 if these two fractal dimensions are obtained before contact deformation. In the present study, D, G, and Ds are considered to be varying with the mean separation (or the interference at the rough surface) between two contact surfaces. The D-Ds relationships for the contacts at the elastic, elastoplastic, and fully plastic deformations are derived and the inceptions of the elastoplastic deformation regime and the fully plastic deformation regime are redefined using the equality of two expressions established in two different ways for the number of contact spots (N). The contact parameters, including the total contact force and the real contact area, were evaluated when the size distribution functions (n) for the three deformation regimes were available. The results indicate that both the D and Ds parameters in these deformation regimes increased with increasing the mean separation (d*). The initial plasticity index before contact deformation (ψ)0 is also a factor of importance to the predictions of the contact load (F*t) and contact area (At*) between the model of variable D and G, non-Gaussian asperity heights and circular contact area and the present model of variable D and G, non-Gaussian asperity heights and fractal contact area.
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Bartram, Lyn, i Colin Ware. "Filtering and Brushing with Motion". Information Visualization 1, nr 1 (marzec 2002): 66–79. http://dx.doi.org/10.1057/palgrave.ivs.9500005.
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Visualizing information in user interfaces to complex, large-scale systems is difficult due to visual fragmentation caused by an enormous amount of inter-related data distributed across multiple views. New display dimensions are required to help the user visually integrate and filter such spatially distributed and heterogeneous information. Motion holds promise in this regard as a perceptually efficient display dimension. It has long been known to have a strong grouping effect, suggesting it has potential for filtering and brushing techniques. However, there is little known about which properties of motion are most effective. This paper reviews the prior literature relating to the use of motion for display and discusses the requirements for how motion can be usefully applied to these problems, especially for visualizations incorporating multiple groups of data objects. Results from previous research by the authors suggested motion type was a strong distinguishing feature. Three types of motions in pairwise combinations were compared: linear, circular and expansion/contraction. Combinations of linear directions were also compared to evaluate how great angular separation needs to be to enforce perceptual distinction. The results showed that motion can effectively group objects that are otherwise dissimilar. Type differentiation is more effective than directional differences (except for 90°). Of the three types studied, circular demands the most attention. Angular separation must be 90° to be equally effective. These results suggest that motion can be usefully applied to both filtering and brushing. They also provide the beginnings of a vocabulary of simple motions that can be applied to information visualization.
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Zhang, Hui, Zixin Liu i Jun Zhang. "An efficient finite element method based on dimension reduction scheme for a fourth-order Steklov eigenvalue problem". Open Mathematics 20, nr 1 (1.01.2022): 666–81. http://dx.doi.org/10.1515/math-2022-0032.
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Abstract In this article, an effective finite element method based on dimension reduction scheme is proposed for a fourth-order Steklov eigenvalue problem in a circular domain. By using the Fourier basis function expansion and variable separation technique, the original problem is transformed into a series of radial one-dimensional eigenvalue problems with boundary eigenvalue. Then we introduce essential polar conditions and establish the discrete variational form for each radial one-dimensional eigenvalue problem. Based on the minimax principle and the approximation property of the interpolation operator, we prove the error estimates of approximation eigenvalues. Finally, some numerical experiments are provided, and the numerical results show the efficiency of the proposed algorithm.
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Yon, Hamizan, Nurul Huda Abd Rahman, Mohd Aziz Aris, Mohd Haizal Jamaluddin, Irene Kong Cheh Lin, Hadi Jumaat, Fatimah Nur Mohd Redzwan i Yoshihide Yamada. "Development of C-Shaped Parasitic MIMO Antennas for Mutual Coupling Reduction". Electronics 10, nr 19 (7.10.2021): 2431. http://dx.doi.org/10.3390/electronics10192431.
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In the 5G system, multiple-input multiple-output (MIMO) antennas for both transmitting and receiving ends are required. However, the design of MIMO antennas at the 5G upper band is challenging due to the mutual coupling issues. Many techniques have been proposed to improve antenna isolation; however, some of the designs have impacts on the antenna performance, especially on the gain and bandwidth reduction, or an increase in the overall size. Thus, a design with a detailed trade-off study must be implemented. This article proposes a new C-shaped parasitic structure around a main circular radiating patch of a MIMO antenna at 16 GHz with enhanced isolation features. The proposed antenna comprises two elements with a separation of 0.32λ edge to edge between radiation parts placed in a linear configuration with an overall dimension of 15 mm × 26 mm. The C-shaped parasitic element was introduced around the main radiating antenna for better isolation. Based on the measurement results, the proposed structure significantly improved the isolation from −23.86 dB to −32.32 dB and increased the bandwidth from 1150 MHz to 1400 MHz. For validation, the envelope correlation coefficient (ECC) and the diversity gain (DG) were also measuredas 0.148 dB and 9.89 dB, respectively. Other parameters, such as the radiation pattern, the total average reflection coefficient and the mean effective gain, were also calculated to ensure the validity of the proposed structure. Based on the design work and analysis, the proposed structure was proven to improve the antenna isolation and increase the bandwidth, while maintaining the small overall dimension.
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Zabala-Quintero, Camilo, Jesus Ramirez-Pastran i Maria Josefina Torres. "Performance Characterization of a New Model for a Cyclone Separator of Particles Using Computational Fluid Dynamics". Applied Sciences 11, nr 12 (9.06.2021): 5342. http://dx.doi.org/10.3390/app11125342.
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In the present study, through Computational Fluid Dynamics techniques, the performance characterization of a new Stairmand-type separator cyclone was carried out using the commercial software ANSYS Fluent. Four models for the geometrical cyclone separator were built, namely model A as per the dimensions reported in the literature and models B, C, and D by applying square and circular shape cavities as a passive flow control technique on the surface of its cylindrical section. The Navier-Stokes equations with the RSM turbulence model were formulated to solve the continuous phase of the cyclone separator and, the Lagrangian approach was adopted to track the solid particles with one way-coupling. The proposed model’s separation efficiency and pressure drop were compared against those recorded in the previous studies reported in the literature. Model D was the cyclone separator that stood out as the most valuable by demonstrating a separation efficiency and pressure drop decrement of 0.42% and 6.01%, respectively.
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VERHOFF, A. "Two-dimensional potential flow solutions with separation". Journal of Fluid Mechanics 657 (21.07.2010): 238–64. http://dx.doi.org/10.1017/s0022112010001448.
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A procedure for constructing two-dimensional incompressible potential flowfield solutions with separation and a recirculation region is presented. It naturally makes use of complex variable theory and other analysis techniques such as conformal mapping and the generalized Poisson integral formula. Flowfield determination is reduced to solution of a boundary value problem in various simple domains. The entire velocity field is described analytically; stream function and velocity potential contour maps are readily constructed. Example solutions are presented. Solutions for sharp leading edge airfoils at arbitrary angle of attack are completely determined, including the limiting angle of attack for upper-surface flow re-attachment. For other configurations (e.g. circular cylinder, backward-facing step) the analytical solution contains one or more free parameters, whose values may be inferred from boundary layer theory or experiment.
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Xue, Xiao Feng, Hua Bai, Yu Li, Wei Li i Sai Gong. "Test Study on Aerodynamic Performance of Three-Dimensional Stayed Cables in Two-Dimensional Flow Field". Advanced Materials Research 532-533 (czerwiec 2012): 469–73. http://dx.doi.org/10.4028/www.scientific.net/amr.532-533.469.
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Cables, distributed with diversity spatially angle, are rich in wind direction. Circular cross sectional shape is sensitive to the Reynolds number. This paper studed the aerodynamic performance of three-dimentional stayed cable under two-dimensional flow field in Chang'an University wind tunnel by Pitot tube, electronic pressure scanning valve, data conversion and collection systems. The following conclusions are obtained: (1)The stagnation point and the upper and lower airflow separation point clockwise goes on with the wind angle increases. Absolute value of pressure coefficient at stagnation point and separation point are biggest at 0°wind angle.(2)The absolute value of pressure coefficient at upper and lower separation point increase with the increase of wind speed.(3) Pressure stagnation point,and upper and lower airflow separation point don’t changed with the parameters of helix,while pressures near helix changed irregularlly. Drag coefficient decrease with the increase of helix distance and the deduce of helix height. Meaningful references are provided for the further refinement research on aerodynamic performance of cable-stayed with suppressing vibration measures.
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Jabbar, Tahseen, Rafi M. Qasim i Bassam A. Mohammed. "Vane Angle Influence on the Flow Pattern around a Circular Pier". U.Porto Journal of Engineering 8, nr 6 (28.11.2022): 189–209. http://dx.doi.org/10.24840/2183-6493_008.006_0014.
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This paper intends to numerically analyze the hydrodynamic characteristics of the flow pattern that surrounds the circular pier near the vane angle. These include flow velocity, turbulent intensity, and pressure. A computational fluid dynamic is proposed to simulate the two-dimensional model by using the finite volume method, while the k - ε turbulence model is used to describe the turbulent model. The vane is located upstream of the pier, with its dimensions as function of the pier diameter. The distance between the vane and the pier center is equal to the pier diameter, the angle of the vane is put with a range from 60o to 180o, and the pier diameter is equal to 10 mm. The turbulent flow has a Reynolds number that varies from 20000 to 50000. The existence of the vane angle leads to two different processes, which are flow separation and flow dissipation, which have a direct effect on flow velocity, turbulent intensity, and pressure. From the current numerical results, the relationships between Reynolds number and average flow velocity, maximum flow velocity, turbulent intensity, and maximum turbulent intensity are more sensitive to flow separation and flow dissipation along the vane. Also, positive and negative pressure distributions have a higher influence on flow separation and flow dissipation.
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Chang, Hsuan-Ting, Tzu-Yao Lin, Chih-Hao Chuang, Chien-Yu Chen, Chian C. Ho i Chuan-Yu Chang. "Separation of Two-Dimensional Mixed Circular Fringe Patterns Based on Spectral Projection Property in Fractional Fourier Transform Domain". Applied Sciences 11, nr 2 (18.01.2021): 859. http://dx.doi.org/10.3390/app11020859.
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In this paper, a method for automatically separating the mixed circular fringe patterns based on the fractional Fourier transform (FrFT) analysis is proposed. Considering the mixed two-dimensional (2-D) Gaussian-based circular fringe patterns, detected by using an image sensor, we propose a method that can efficiently determine the number and parameters of each separated fringe patterns by using the FrFT due to the observed higher sparsity in the frequency domain than that in the spatial domain. First, we review the theory of FrFT and the properties of the 2-D circular fringe patterns. By searching the spectral intensities of the various fractional orders in the FrFT projected along both the frequency axes, the proposed method can automatically determine the total fringe number, the central position, binary phase, and the maximum fringe width of each 2-D circular fringe pattern. In the experimental results, both the computer-simulated and optically mixed fringe patterns are used to verify the proposed method. In addition, the additive Gaussian noise effects on the proposed method are investigated. The proposed method can still successfully separate the mixed fringe pattern when the signal-to-noise ratio is higher than 7 dB.
Rozprawy doktorskie na temat "Circular separation dimension"
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MOREAU, FRANCOISE. "Etude de la serie cellulaire, bidimensionnelle et complexe, et de ses applications aux ecoulements de stokes en canal plan". Poitiers, 1988. http://www.theses.fr/1988POIT2278.
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Etude numerique d'ecoulements plans permanents de stokes qui s'etablissent dans un canal rectiligne illimite sous l'action de sources de mouvement variees (1 ou 2 cylindres de rayons, emplacements et mouvements divers). A faible distance de ces sources, le fluide decolle des parois pour former une suite de cellules visqueuses dont on analyse la structure et les particularites geometriques. Calculs bases sur la methode des moindres carres
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Hellou, Mustapha. "Etude numérique et expérimentale de l'écoulement à structure cellulaire engendré par la rotation d'un cylindre dans un canal". Poitiers, 1988. http://www.theses.fr/1988POIT2267.
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Etude du decollement de l'ecoulement et de la formation de cellules. Structure et caracteristiques geometriques de ces cellules. Analyse du champ hydrodynamique. Calcul numerique base sur l'ecriture des conditions des conditions aux limites par la methode des moindres carres. Mise au point d'une technique de visualisation par intermittence pendant de longues durees, utilisant les traceurs solides
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Lahiri, Abhiruk. "Problems on bend-number, circular separation dimension and maximum edge 2-colouring". Thesis, 2018. https://etd.iisc.ac.in/handle/2005/5491.
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Representation of graphs as the intersection graphs of geometric objects has a long
history. The objective is to a nd a collection of \simple" sets S such that a given graph
G is its intersection graph. We are interested in two types of intersection representations
motivated by VLSI circuit layout problem. In these models, vertices are represented by
polygonal paths with alternating horizontal and vertical segments. The measure of the
complexity of a path is de fined by the number of bends it has. The objective is to minimise
the maximum number of bends used by any path in a representation. This minimum number
(over all possible representations) is called the bend number of the graph.
In the first model, two vertices share an edge if and only if corresponding paths intersect.
A graph that can be represented in such a way is called a VPG graph. We study a subclass
of the planar graphs on this model. In the second model, two vertices of the graph share an
edge if and only if corresponding paths overlap on a non-zero length segment. A graph that
can be represented in such a way is called an EPG graph. We study Halin graphs which is
a subclass of the planar graphs, fully subdivided graphs and minimally 2-connected graphs
for this model. Using one of these results, we show optimization problems such as maximum
independent set, minimum dominating set are APX-hard on 1-bend EPG graphs. We devise
a polynomial time algorithm for the colouring and maximum independent set problem on
two-sided boundary generated EPG graphs which is a subclass of 1-bend EPG graphs. We
also establish NP-hardness and inapproximability result on three-sided boundary generated
EPG graphs and four-sided boundary generated EPG graphs.
In the second part, we study the notion of circular separation dimension which was
introduced recently by Douglas West. Formally, a pair of non-adjacent edges is said to be
separated in a circular ordering of vertices if the endpoints of the two edges do not alternate
in the ordering. The circular separation dimension (CSD) of a graph G is the minimum
number of circular orderings of the vertices of G such that every pair of non-adjacent edges
is separated in at least one of the circular orderings. We establish a new upper bound for
CSD in terms of the chromatic number of the graph. We further study this question for
special graph classes such as series-parallel graphs and two-outerplanar graphs.
In the nal part, we study maximum edge 2-colouring problem. For a graph G, the
maximum edge 2-colouring problem seeks the maximum possible colours that can be used
to colour the edges of the graph such that edges incident on a vertex span at most two distinct
colours. The problem is well studied in combinatorics, in the context of the anti-Ramsey
number. Algorithmically, the problem is known to be NP-hard. It is also known that no
polynomial time algorithm can approximate to a factor less than 3=2 assuming the unique
game conjecture. The obvious but the only known algorithm issues different colours to the
edges of a maximum matching and different colours to remaining connected components.
We establish an improved approximation bound of 8=5 for the algorithm, for triangle-free
graphs with perfect matching.
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CHEN, CHIEN FAN, i 陳建帆. "2-Dimension incompressible boundary-layer separation over circular cylinder in uniform shear flow". Thesis, 1997. http://ndltd.ncl.edu.tw/handle/63105155668955944470.
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碩士國立臺灣大學
機械工程學系
85
The present research studies the separation of boundary-layer over a circularcylinder placed in a uniform shear flow.In steady case, the steady version ofthe boundary-layer equations are solved numerical via the conventionalspace-marching technique. Calculated results shows that with increasing shear rate of the free stream, the location of separation at the upper half of the cylinder(i.e. the side of the cylinder with larger free stream velocity)shiftsslightly towards the upstream direction.While at the lower half of the cylinder,a critical value is obtained.When the shear rate of the free stream increasesbeyond this critical value,separation point will jump from the rear part ofthe cylinder to the windward side of the cylinder and continue to move in the upstream direction. In unsteady case, the governing equations are solved byusing an implicit time advancing technique.Calculations show that unsteady separation first appears in the upper side of the cylinder, that is the sideof the cylinder with larger free stream velocity distribution, regardless thevalue of the shear rate . The separation time is found to be promoted withincreasing shear rate, and the separation location also shifts toward the leading edge as shear rate increases. The results are also confirmed by the Lagrangian calculations.
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Lai, Chang-Sheng, i 賴昶勝. "Localization and Separation of Acoustic Sources by Using a 2.5-Dimensional Circular Microphone Array". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/wg7yvf.
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碩士國立清華大學
動力機械工程學系
105
Circular microphone arrays (CMA) are preferred over more complex spherical microphone arrays (SMA) in the context of some audio applications because azimuthal angles of spatial sound are considered more important than the elevation angles in those scenarios. However, the fact that CMA does not resolve the elevation angle well can be a limitation for some applications which involves 3-dimensional sound fields. But this can also be a limitation in spatial audio rendering. Sources with elevation less than 60 degrees can be localized precisely respectively. This paper proposes a 2.5-dimensional (2.5-D) CMA that consists of an unbaffled CMA and a vertical logarithmic-spacing linear array on the top. In the localization stage, two delay-and-sum (DAS) beamformers are applied to the circular array and the linear array, respectively. The product of the identified angular patterns yields the direction of arrival (DOA). In the separation stage, Tikhonov Regularization (TIKR) and Compressive Sensing (CS) are employed to extract the source signal amplitudes from the output signals from two arrays. The extracted signals are further processed by Normalized Least-Mean-Square (NLMS) algorithm with Internal Iteration (IIT) Algorithm respectively in order to produce the source signal with improved quality. To validate the 2.5-D CMA experimentally, a three-dimensionally printed circular array comprised of a 24 micro-electro-mechanical-system (MEMS) microphone circular array and an 8- MEMS microphone logarithmic-spacing linear array is constructed for localization and separation for sound sources. Objective Perceptual Evaluation of Speech Quality (PESQ) test and a subjective listening test are undertaken in performance evaluation. The experimental results demonstrate better separation quality achieved by the CS combined with NLMS method than by the TIKR combined with NLMS method.
Części książek na temat "Circular separation dimension"
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De Martino, Paolo. "Towards Circular Port–City Territories". W Regenerative Territories, 161–71. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-78536-9_10.
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AbstractPort and city authorities all over Europe and beyond are striving with finding solutions able to combine sustainability with economic growth. Several global urgencies in fact, such as climate change, energy transition, the exponential changes in the scale of ports and ships and last but not least the economic and health shock related to the coronavirus pandemic, are challenging the spaces where ports physically meet their cities, generating processes of caesura within the urban patterns with consequent impacts on the quality of life. In port cities, infrastructures and energy flows overlap with city flows and patterns that change with different rhythms and temporalities. This discrepancy creates abandonment and marginality between port and city. This today is no longer sustainable. New approaches and solutions that look at integration and circularity rather than separation are necessary.Circularity has been widely discussed in the literature. However, the concept still remains very controversial, especially when it comes to port cities where new definitions are needed in particular to better understand the spatial dimension of circularity. The Rotterdam therefore case study stands exemplary. Here, the concept of the circular economy refers mostly to the theme of obsolete industrial buildings and marginal that are reinserted again within the urban metabolism. The case of Rotterdam points out that the competition of the port today goes through the quality of its relationship spaces and the ability of the different actors involved in the planning process to hold together economic growth and environmental sustainability. The areas along the river are in fact the most fascinating places in the city and today they are ready for a different use. In order for the city to become an attractive place to live it is necessary to build new, innovative and sustainable spatial visions. This will lead to scenarios of sustainable coexistence between port and city. Therefore, these two agendas (sustainable port and city attractiveness) came together in the area known as Makers district (M4H) which, together with RDM campus, represents the Rotterdam testing ground for innovation.Therefore, this chapter, by arguing that ports will play a crucial role in the transition towards more circularity investigates how to make it happen and how to transform the challenges of the port into opportunities for a territorial regeneration towards new forms of integration. In order to answer the question, the case of Rotterdam is presented to analyse a model of urban regeneration where different planning agencies—mainly port authority, municipality, universities and private parties—work together at different scales to define a sustainable coexistence of interests. The research, which draws data on existing literature and policy documents analysis, firstly introduces the spatial and governance structures of the city of Rotterdam as part of a bigger metropolitan region. Secondly, it analyses the case of “Stadshavens strategy” as an emblematic example to overcome conflicts and path dependencies at the intersection of land and water. Finally, it concludes by highlighting some limitations and path dependencies that could make the transition to new forms of the circular economy very difficult in the future.
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Garrett, Steven L. "Three-Dimensional Enclosures". W Understanding Acoustics, 621–72. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-44787-8_13.
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Abstract In this chapter, solutions to the wave equation that satisfies the boundary conditions within three-dimensional enclosures of different shapes are derived. This treatment is very similar to the two-dimensional solutions for waves on a membrane of Chap. 10.1007/978-3-030-44787-8_6. Many of the concepts introduced in Sect. 10.1007/978-3-030-44787-8_6#Sec1 for rectangular membranes and Sect. 10.1007/978-3-030-44787-8_6#Sec5 for circular membranes are repeated here with only slight modifications. These concepts include separation of variables, normal modes, modal degeneracy, and density of modes, as well as adiabatic invariance and the splitting of degenerate modes by perturbations. Throughout this chapter, familiarity with the results of Chap. 10.1007/978-3-030-44787-8_6 will be assumed. The similarities between the standing-wave solutions within enclosures of different shapes are stressed. At high enough frequencies, where the individual modes overlap, statistical energy analysis will be introduced to describe the diffuse (reverberant) sound field.
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Gölling, Burkhard. "Experimental Investigations of Separating Boundary-Layer Flow from Circular Cylinder at Reynolds Numbers from 105 up to 107 three-dimensional Vortex Flow of a Circular Cylinder)". W Solid mechanics and its applications, 455–62. Dordrecht: Springer Netherlands, 2006. http://dx.doi.org/10.1007/978-1-4020-4150-1_44.
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Steward, David R. "Analytic Elements from Separation of Variables". W Analytic Element Method, 165–226. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198856788.003.0004.
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Separation of variables provides influence functions for analytic elements, which extend the solutions available with complex functions to problems involving the Helmholtz and modified Helmholtz equations. Methods are introduced for one-dimensional problems that provide the background vector field for many problems, and these solutions are extended to finite domains with interconnected rectangle elements in Section 4.3. Circular elements are developed in Section 4.4 using series of Bessel and Fourier functions to model wave propagation around and through collections of elements, and vadose zone solutions are extended to solve the nonlinear interface conditions occurring along circles. Methods are extended to three-dimensional problems for spheres (Section 4.5), and prolate and oblate spheroids in Section 4.6.
Streszczenia konferencji na temat "Circular separation dimension"
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Liou, Jen Luen, i Jen Fin Lin. "A Microcontact Model Developed for Asperity Heights With a Variable Profile Fractal Dimension, a Surface Fractal Dimension, Topothesy, and Non-Gaussian Distribution". W STLE/ASME 2008 International Joint Tribology Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/ijtc2008-71086.
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The cross sections formed by the contact asperities of two rough surfaces at an interference are island-shaped, rather than having the commonly assumed circular contour. These island-shaped contact surface contours show fractal behavior with a profile fractal dimension Ds. The surface fractal dimension for the asperity heights is defined as D and the topothesy is defined as G. In the study of Mandelbrot, the relationship between D and Ds was given as D = Ds+1 if these two fractal dimensions are obtained before contact deformation. In the present study, D, G, and Ds are considered to be varying with the mean separation (or the interference at the rough surface) between two contact surfaces. The D-Ds relationships for the contacts at the elastic, elastoplastic, and fully plastic deformations are derived and the inceptions of the elastoplastic deformation regime and the fully plastic deformation regime are redefined using the equality of two expressions established in two different ways for the number of contact spots (N).
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Yamada, Shunsuke, Koui Shibata, Hikaru Yanagihara, Takahiro Doi, Hitoshi Ishikawa i Takehiko Segawa. "Wake Structure Behind Circular Cylinder by Plasma Actuators". W ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-13015.
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The separation flow causes the decrease of the driving efficiency of the fluid machines. It is important to control the separation on the bluff body, boundary layer and so on. The purpose of the present study is to control the separation on a circular cylinder and investigate the wake structure using the induced by dielectric barrier discharge (DBD) plasma. The electrode of the DBD plasma was mounted. In previous study, it is reported that the three dimensional wake structures are effective for the drag reduction. We investigate the three dimensional structure of the wake due to three dimensional jets of plasma actuators. The plasma actuators have pulse driving frequency of 0, 0.22, 1.0 and 2.0. A voltage of 4 kVpp and a frequency of 10 kHz are applied to the electrode. The velocity profiles behind the circular cylinder were measured by X type hot-wire anemometer at a Reynolds number of 1.0 × 103. The wake structure changes because the roll up of vortex is suppressed using pulse driving of the plasma actuators. The effect of plasma actuators is evaluated based on the half width and Reynolds stress in the wake.
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Ishii, Michiharu, Xiao Feng Yang, Masaharu Matsubara, Yoshiaki Tsuchiya i Takashi Yoshida. "Experimental Study of a Rectangular Jet Impinging on a Circular Cylinder". W ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45195.
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It was known that development of a jet from a rectangular orifice could be divided into three regions, which are 1) potential core region 2) characteristic decay region and 3) axisymmetric decay region. When a circular cylinder is placed in the rectangular jet, characteristic separation occurs around the cylinder and shapes of non-separation area on the cylinder are distinguished with the streamwise position of the cylinder. This flow geometry can be frequently seen in the industrial applications and drag and heat transfer of the cylinder would be important for the designs. In this study the rectangular jet impinging on a circular cylinder has been experimentally investigated. The relation between the jet development before impinging and separation area on the cylinder is especially focused. In the case that the cylinder is in the potential core region, the non-separation area distributes as saddle shape and the spanwise pressure distribution at the impinging line on the cylinder is almost constant around jet center and in the edge of jet impinging region it decreases with the distance. Then the pressure reaches at the minimum in the outside of the edge and recovers to the pressure of the circumference far from the edge. This pressure distribution suggests that flow just above the impinging line of cylinder blows toward the center and that the impinging flow is incredibly three-dimensional. When the cylinder is in the characteristic decay region, the non-separation area distributes as saddle shape as well as in the case of the potential core region. The spanwise impinging pressure distribution on the cylinder has maximums at the spanwise edges of impinging jet and sudden decrease out side of the jet. In this case the minima in the fringes of the jet were not observed. In the case of the axisymmetric region, the area of non-separation is elliptic and at the spanwise center the non-separated flow reaches backside of the cylinder.
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Anand, K., S. Sarkar i N. Thilakan. "Experiments on Leading-Edge Induced Separated Shear Layer Under Various Imposed Pressure Gradients". W ASME 2014 Gas Turbine India Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gtindia2014-8177.
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The behaviour of a separated shear layer past a semi-circular leading edge flat plate, its transition and reattachment downstream to separation are investigated for different imposed pressure gradients. The experiments are carried out in a blowing tunnel for a Reynolds number of 2.44×105 (based on chord and free-stream velocity). The mean flow characteristics and the instantaneous vector field are documented using a two-component LDA and a planar PIV, whereas, surface pressures are measured with Electronically scanned pressure (ESP). The onset of separation occurs near the blend point for all values of β (flap angle deflection), however, a considerable shift is noticed in the point of reattachment. The dimensions of the separation bubble is highly susceptible to β and plays an important role in the activity of the outer shear layer. Instantaneous results from PIV show a significant unsteadiness in the shear layer at about 30% of the bubble length, which is further amplified in the second half of the bubble leading to three-dimensional motions. The reverse flow velocity is higher for a favourable pressure gradient (β = +30°) and is found to be 21% of the free stream velocity. The Reynolds number calculated based on ll (laminar shear layer length), falls in the range of 0.9×104 to 1.4×104. The numerical values concerning the criterion for separation and reattachment agree well with the available literature.
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Samson, A., i S. Sarkar. "Aerodynamic Measurements on the Interaction of Secondary Jets and Separation Bubble". W ASME 2012 Gas Turbine India Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gtindia2012-9537.
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The dynamics of separation bubble under the influence of continuous jets ejected near the semi-circular leading edge of a flat plate is presented. Two different streamwise injection angles 30° and 60° and velocity ratios 0.5 and 1 for Re = 25000 and 55000 (based on the leading-edge diameter) are considered here. The flow visualizations illustrating jet and separated layer interactions have been carried out with PIV. The objective of this study is to understand the mutual interactions of separation bubble and the injected jets. It is observed that flow separates at the blending point of semi-circular arc and flat plate. The separated shear layer is laminar up to 20% of separation length after which perturbations are amplified and grows in the second-half of the bubble leading to breakdown and reattachment. Blowing has significantly affected the bubble length and thus, turbulence generation. Instantaneous flow visualizations supports the unsteadiness and development of three-dimensional motions leading to formation of Kelvin-Helmholtz rolls and shedding of large-scale vortices due to jet and bubble interactions. In turn, it has been seen that both the spanwise and streamwise dilution of injected air is highly influenced by the separation bubble.
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Pradeep, A. M., i R. K. Sullerey. "Active Separation Control in Circular and Transitioning S-Duct Diffusers Using Vortex Generator Jets". W ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/fedsm2006-98391.
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Performance enhancement of three-dimensional S-duct diffusers by separation control using vortex generator jets is the objective of the current experimental investigation. Two different diffuser geometries namely, a circular diffuser and a rectangular–to–circular transitioning diffuser were studied in uniform inflow conditions at a Reynolds number of 7.8 × 105 and the performance evaluation of the diffusers was carried out in terms of static pressure improvement and quality (flow uniformity) of the exit flow. Detailed measurements that included total pressure, velocity distribution, surface static pressure, skin friction and boundary layer measurements were taken and these results are presented here in terms of static pressure rise, distortion coefficient and total pressure loss coefficient at the duct exit. The mass flow rate of the air injected through the VGJ was about 0.06 percent of the main flow for separation control. The distortion coefficient reduced by over 25 percent and the total pressure loss coefficient reduced by about 30 percent in both the diffusers. The physical mechanism of the flow control devices used has been explored using smoke visualization images.
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Mariotti, Alessandro, Guido Buresti i Maria Vittoria Salvetti. "Flow Separation Control and Drag Reduction for a Two-Dimensional Boat-Tailed Bluff Body Through Transverse Grooves". W ASME 2018 5th Joint US-European Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/fedsm2018-83458.
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The present work focuses on a passive strategy consisting in the introduction of properly contoured transverse grooves to delay the flow separation occurring on a boat-tailed bluff body before its sharp-edged base. We consider a two-dimensional body having a cross-section with a 3:1 elliptical forebody and a rectangular main part followed by a circular-arc boat tail. We carry out Variational Multiscale Large Eddy Simulations at Re = Du∞/v = 9.6 × 104. A boat-tail drag reduction of the order of 9.7% is produced by the significant delay of the flow separation caused by the groove and by the consequent increase of the base pressure. This effect is mainly due to the relaxation of the no-slip condition over the small and steady recirculation region inside the groove, which reduces the momentum losses near the wall and thus delays boundary layer separation. The flow control device is also robust to small variations of the groove location and depth.
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Agelinchaab, M., i M. F. Tachie. "Separated and Reattached Flow Over Square, Rectangular and Semi-Circular Blocks". W ASME/JSME 2007 5th Joint Fluids Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/fedsm2007-37246.
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A particle image velocimetry is used to study the characteristics of separated and reattached turbulent flow over two-dimensional transverse blocks of square, rectangular and semi-circular cross-sections fixed to the bottom wall of an open channel. The ratio of upstream boundary layer thickness to block height is considerably higher than in prior studies. The results show that the mean and turbulent statistics in the recirculation region and downstream of reattachment are significantly different from the upstream boundary layer. The variation of the Reynolds stresses along the separating streamlines is discussed within the context of vortex stretching, longitudinal strain rate and wall damping. It appears wall damping is a more dominant mechanism in the vicinity of reattachment. The levels of turbulence diffusion and production by the normal stresses are significantly higher than in classical turbulent boundary layers. The bulk of turbulence production occurs in mid-layer and transported into the inner and outer layers. The results also reveal that the curvature of separating streamline, separating bubble beneath it as well as the mean velocity and turbulent quantities depend strongly on block geometry.
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Ghosh, S. K., S. K. Mukherjea i B. N. Datta. "Study of the Effect of Tangential Point Blowing on the Incompressible Boundary Layer Flow Around a Circular Cylinder". W ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-37898.
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In the present work, two dimensional flow simulations have been performed to study the effect of tangential blowing on the drag force for the case of flow around a circular cylinder only at Reynolds number (Re) 200. Blowing ports have been placed symmetrically with respect to the horizontal flow axis. The effect of blowing on the boundary layer has been studied with respect to the intensity of blowing as well as port position of blowing. For a particular intensity of blowing, oscillations of the front stagnation point and the separation point was studied. It was found that oscillation frequencies were identical with that of lift coefficient. It was also observed that with the increase of the intensity of the blowing the position of the separation point shifts downstream (separation delay)thus the wake becomes narrower resulting the decrease of drag. Strouhal number was found to increase with the intensity of blowing. It was observed that the Strouhal number as well as the position of the separation point is influenced by the position of the blowing port. Although, for a significant range of the blowing port positions the Strouhal number is observed to be constant. Drag was found to be influenced by the position of the blowing ports. Pressure drag was found to be more significant. Thus total drag is influenced primarily by the pressure drag. It was observed that in the range of 40° to about 110° for the position of the blowing port drag decreased. But beyond 110° it increased again.
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Lee, Sang Woo, Seong Kuk Joo i Joon Sik Lee. "Flow Characteristics Inside Circular Injection Holes Normally Oriented to a Crossflow: Part II — Three Dimensional Flow Data and Aerodynamic Loss". W ASME Turbo Expo 2000: Power for Land, Sea, and Air. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/2000-gt-0257.
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Presented are three-dimensional mean velocity components and aerodynamic loss data inside circular injection holes. The holes are normally oriented to a crossflow and each hole has a sharp square-edged inlet. Because of their importance to flow behavior, three different blowing ratios of M = 0.5, 1.0 and 2.0, and the hole length-to-diameter ratios of L/D = 0.5, 1.0 and 2.0 are investigated. The entry flow is characterized by a separation bubble, meanwhile the exit flow by the direct interaction with the crossflow. The uniform on-coming flow at the inlet undergoes a strong acceleration and a subsequent gradual deceleration along a converging-diverging flow passage formed by the inlet separation bubble. After passing the throat of the converging-diverging passage, the potential-core flow which is nearly axisymmetric decelerates on the windward side, but tends to accelerate on the leeward side. The presence of the crossflow thus reduces the discharge of the injectant on the windward side, but enhances its efflux on the leeward side. This trend is greatly accentuated at M = 0.5. In general, there are strong secondary flows in the inlet and exit planes of the injection hole. The secondary flow within the injection hole, on the other hand, is found relatively weak. The inlet secondary flow is characterized by a strong inward flow toward the injection-hole center. However, it is not completely directed inward since the crossflow effect is superimposed on it. Past the throat, the secondary flow is observed such that the leeward velocity component induced by the crossflow is superimposed on the diverging flow. Short L/D usually results in the exit discharging flow with a steep velocity gradient as well as a strong deceleration on the windward side, as low M does. The aerodynamic loss inside the injection hole is originated from the inlet separation bubble, wall friction and interaction of the injectant with the crossflow. The first one is considered as the most dominant source of loss, even in the case of L/D = 2.0. At L/D = 0.5, the first and third sources are strongly coupled with each other. Regardless of L/D, the mass-averaged aerodynamic loss coefficient has an increasing tendency with increasing M.