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High Quality Content by WIKIPEDIA articles! Seaplanes, flying boats, and amphibious aircraft are designed to take off and land on water. Landing can be supported by a hull-shaped fuselage and/or pontoons. The availability of a long effective runway was historically important on lifting size restrictions on aircraft, and their freedom from constructed strips remains useful for transportation to lakes and other remote areas. The ability to loiter on water is also important for marine rescue operations and fire fighting. One disadvantage of water landing is that it is dangerous in the presence of waves. Furthermore, the necessary equipment compromises the craft's aerodynamic efficiency and speed.

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This work presents the rigorous numerical analysis of the aerodynamic noise generation via Lighthill acoustic analogy, which is a non-homogeneous wave equation describing the sound waves. Over more than five decades, the Lighthill analogy was extensively used as one of the major tools in engineering applications in acoustics. However, the first mathematical research of the Finite Element approximation for it is introduced here. Specifically, the focus is on both Direct Numerical and Large Eddy Simulations. The semidiscrete and fully discrete Finite Element methods in DNS are presented. Also, three independent ways of computing the sound power in the semidiscrete case in DNS are introduced. All of these methods are based on the Finite Element scheme. The methods are compared from the point of view of computational cost, accuracy and simplicity. Finally, the concept of Large Eddy Simulation is introduced for aeroacoustic research via Lighthill analogy. Two subgrid scale models are presented for the filtered acoustic analogy. The semidiscrete Finite Elemet Method is analyzed for both. The computational experiments are presented.

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Aero-acoustics refers to the branch of acoustics that studies sonic waves generated via either turbulent air flows or aerodynamic forces interacting with surfaces. Although the problem of sound waves propagation in a transverse shear flow seems to be fully investigated and solved, considering that, Musafir identified, through a general scheme for representing solutions of Lilley's equation, that some results in Scott's solution for a point quadrupole source in the bi-dimensional linear shear layer are incorrect. The research presented in this book makes an effort at 1) revisiting the problem of propagation of the sound waves emitted from various point sources through a bi-dimensional linear shear layer in order to verify, by comparing the correct quadrupole solution with the one obtained by Scott, 2) studying to which extent conclusions drawn by Scott's based on his results are correct or should be altered. The theory is complemented by Matlab codes and case studies, implementing the exact and approximate solutions for different multipole sources close to a linear shear layer. The cases of source located in the uniform flow region and in the shear layer itself will be considered.

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Conformal components are used nowadays at higher rate than ever before. They can be found in curved mobile phones, communication, navigation, and imaging systems in land, water, air, and space vehicles. The integration of those components within the external structure became of significant importance for aerodynamic, electromagnetic, aesthetic, orphysical reasons. As a result, many mathematical models were previously developed to analyze and optimize such conformed devices. In this thesis, we contributed to this field by developing various models for full wave analysis of spheroidal components.As a starting point, mathematical formulas for conforming antennas on oblate and prolate spheroids were obtained. Those conformation methods were validated by conforming many antennas on spheroidal surfaces. They were then used to formulate Method of Moments equations with spheroidally curved current functions for analyzing wire antennas of randomshape conformed to spheroids in the frequency domain. The complete model was applied to a conformal Archimedean spiral antenna on an oblate spheroid and showed that the conformed spiral has similar current distribution as its planar counterpart but produces an unsymmetrical radiation pattern. The obtained model was then extended to spheroidal multi-layer structures by integrating the spheroidal dyadic Green’s Function within its mathematical derivation. However, due to a detected divergence in that function, the model couldn’t be implemented.On the side of time based analysis methods, a Finite Difference Time Domain method was developed for closed oblate and prolate spheroidal structures. Alternative formulas for the structure’s singularities and the condition of numerical stability were derived as well. The obtained model was then validated and used to characterize spheroidal cavities in the time and frequency domains. The method was extended later to unbounded spheroidal domain by deriving the Absorbing Boundary Conditions using the One Way Wave method. The whole model was then applied to characterize a patch antenna conformed to a prolate spheroid. Finally, an analytical solution for the transient fields in spherical multilayer media energized by spherical harmonics source and an algorithm for tracing back the path of all the reflected waves were obtained. The model was applied to different multilayer structures where the transient response was obtained and validated against a numerical solution.

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This volume contains the contributions to the 10th International Workshop on Railway Noise, held October 18-22, 2010, in Nagahama, Japan, organized by the Railway Technical Research Institute (RTRI), Japan. With 11 sessions and 3 poster sessions, the workshop featured presentations by international leaders in the field of railway noise and vibration. All subjects relating to 1. prospects, legal regulation, and perception, 2. wheel and rail noise, 3. structure-borne noise and squeal noise, 4. ground-borne vibration, 5. aerodynamic noise and micro-pressure waves from tunnel portals, 6. interior noise and sound barriers, and 7. prediction, measurements, and monitoring are addressed here. This book is a useful "state-of-the-art" reference for scientists and engineers involved in solving environmental problems of railways.

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Anbieter: Orell Fuessli CH

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Transonic flow occurs around moving objects as they approach and cross the sound barrier. Serious problems can occur at this point, such as shock-induced flow separation which can cause the aircraft to spin out of control. Another important practical problem is the achievement of higher aerodynamic performance of aircraft at cruise conditions, which leads to considerable fuel savings. The success in application of numerical methods for simulation of transonic flow and aircraft design depends on developments in the underlying mathematical theory. This book presents a breakthrough in the solvability analysis of boundary value problems, which makes it possible to establish convergence of finite element approximations for shock-free flow and to provide a framework for putting the existing numerical methods on a more sound basis. Also, physical aspects concerned with patterns of formation and propagation of weak shock waves are analysed. This contributes to the understanding of the extreme sensitivity of transonic flow to perturbation of freestream conditions. The developed theoretical knowledge base yields promising concepts of the airfoil design and active flow control by airfoil/wing shape modifications or suction/blowing through a perforated surface. Boundary Value Problems for Transonic Flow * Focuses on Computational Fluid Dynamics. * Addresses practical problems, such as airfoil design and flow control. * Presents developments made in the last two decades. In essence this is a much needed monograph for researchers and engineers in applied mathematics and numerical analysis applied to aerodynamics and for algorithm developers in Computational Fluid Dynamics in the aircraft industry. It gives design engineers the underlying mathematical theory necessary for developing new concepts for airfoil/wing design and flow control.

Anbieter: Orell Fuessli CH

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327,90 CHF *

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This volume contains the contributions to the 10th International Workshop on Railway Noise, held October 18-22, 2010, in Nagahama, Japan, organized by the Railway Technical Research Institute (RTRI), Japan. With 11 sessions and 3 poster sessions, the workshop featured presentations by international leaders in the field of railway noise and vibration. All subjects relating to 1. prospects, legal regulation, and perception; 2. wheel and rail noise; 3. structure-borne noise and squeal noise; 4. ground-borne vibration; 5. aerodynamic noise and micro-pressure waves from tunnel portals; 6. interior noise and sound barriers; and 7. prediction, measurements, and monitoring are addressed here. This book is a useful 'state-of-the-art' reference for scientists and engineers involved in solving environmental problems of railways.

Anbieter: Orell Fuessli CH

Stand: 10.07.2020 Zum Angebot

Stand: 10.07.2020 Zum Angebot