scholarly journals Scattering by a periodic tube in $ \newcommand{\real}{\mathbb{R}} \newcommand{\re}{{\rm Re}} \real^3$ : part ii. A radiation condition

2019 ◽  
Vol 35 (10) ◽  
pp. 104005
Author(s):  
Andreas Kirsch
Keyword(s):  
Radiation Condition ◽  
Periodic Tube

VERY HIGH-ORDER SPATIALLY IMPLICIT SCHEMES FOR COMPUTATIONAL ACOUSTICS ON CURVILINEAR MESHES

2001 ◽  
Vol 09 (04) ◽  
pp. 1259-1286 ◽  
Author(s):  
MIGUEL R. VISBAL ◽  
DATTA V. GAITONDE
Keyword(s):  
Three Dimensional ◽  
Radiation Condition ◽  
Higher Order ◽  
High Order ◽  
High Frequencies ◽  
Decomposition Strategies ◽  
The Impact ◽  
Spurious Modes ◽  
Very High ◽  
Computational Strategy

A high-order compact-differencing and filtering algorithm, coupled with the classical fourth-order Runge–Kutta scheme, is developed and implemented to simulate aeroacoustic phenomena on curvilinear geometries. Several issues pertinent to the use of such schemes are addressed. The impact of mesh stretching in the generation of high-frequency spurious modes is examined and the need for a discriminating higher-order filter procedure is established and resolved. The incorporation of these filtering techniques also permits a robust treatment of outflow radiation condition by taking advantage of energy transfer to high-frequencies caused by rapid mesh stretching. For conditions on the scatterer, higher-order one-sided filter treatments are shown to be superior in terms of accuracy and stability compared to standard explicit variations. Computations demonstrate that these algorithmic components are also crucial to the success of interface treatments created in multi-domain and domain-decomposition strategies. For three-dimensional computations, special metric relations are employed to assure the fidelity of the scheme in highly curvilinear meshes. A variety of problems, including several benchmark computations, demonstrate the success of the overall computational strategy.

scholarly journals The Computation of the Magnitude of the Far Field for an Eccentric Circular Cylinder

2015 ◽  
Vol 2015 ◽  
pp. 1-8
Author(s):  
Bülent Yılmaz
Keyword(s):  
Circular Cylinder ◽  
Plane Wave ◽  
Radiation Condition ◽  
Higher Order ◽  
Numerical Results ◽  
Surface Radiation ◽  
Far Field ◽  
Condition Method ◽  
Radiation Conditions

The specific case of scattering of a plane wave by a two-layered penetrable eccentric circular cylinder has been considered and it is about the validity of the on surface radiation condition method and its applications to the scattering of a plane wave by a two-layered penetrable eccentric circular cylinder. The transformation of the problem of scattering by the eccentric circular cylinder to the problem of scattering by the concentric circular cylinder by using higher order radiation conditions, is observed. Numerical results presented the magnitude of the far field.

Linear and non-linear potential-flow calculations of free-surface waves with lift and induced drag

2000 ◽  
Vol 214 (6) ◽  
pp. 801-812
Author(s):  
C-E Janson
Keyword(s):  
Free Surface ◽  
Potential Flow ◽  
Lift Force ◽  
Radiation Condition ◽  
Linear Potential ◽  
Surface Boundary ◽  
Model Approximation ◽  
Non Linear ◽  
Lifting Surfaces ◽  
The Waves

A potential-flow panel method is used to compute the waves and the lift force from surface-piercing and submerged bodies. In particular the interaction between the waves and the lift produced close to the free surface is studied. Both linear and non-linear free-surface boundary conditions are considered. The potential-flow method is of Rankine-source type using raised source panels on the free surface and a four-point upwind operator to compute the velocity derivatives and to enforce the radiation condition. The lift force is introduced as a dipole distribution on the lifting surfaces and on the trailing wake, together with a flow tangency condition at the trailing edge of the lifting surface. Different approximations for the spanwise circulation distribution at the free surface were tested for a surface-piercing wing and it was concluded that a double-model approximation should be used for low speeds while a single-model, which allows for a vortex at the free surface, was preferred at higher speeds. The lift force and waves from three surface-piercing wings, a hydrofoil and a sailing yacht were computed and compared with measurements and good agreement was obtained.

An Extrapolation Method to Compute Far-Field Pressures From Near-Field Pressures Obtained by Finite Element Method

1995 ◽  
Author(s):  
Jamal Assaad ◽  
Christian Bruneel ◽  
Jean-Michel Rouvaen ◽  
Régis Bossut
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Near Field ◽  
Radiation Condition ◽  
Directivity Pattern ◽  
Extrapolation Method ◽  
External Boundary ◽  
Finite Width ◽  
Far Field ◽  
Element Method

Abstract The finite element method is widely used for the modeling of piezoelectric transducers. With respect to the radiation loading, the fluid is meshed and terminated by an external nonreflecting surface. This reflecting surface can be made up with dipolar damping elements that absorb approximately the outgoing acoustic wave. In fact, with dipolar dampers the fluid mesh can be quite limited. This method can provides a direct computation of the near-field pressure inside the selected external boundary. This paper describes an original extrapolation method to compute far-field pressures from near-field pressures in the two-dimensional (2-D) case. In fact, using the 2-D Helmholtz equation and its solution obeying the Sommerfeld radiation condition, the far-field directivity pattern can be expressed in terms of the near-field directivity pattern. These developments are valid for any radiation problem in 2D. One test example is described which consists of a finite width planar source mounted in a rigid or a soft baffle. Experimental results concerning the far-field directivity pattern of lithium niobate bars (Y-cut) are also presented.

scholarly journals Stable Numerical Evaluation of Finite Hankel Transforms and Their Application

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Manoj P. Tripathi ◽  
B. P. Singh ◽  
Om P. Singh
Keyword(s):  
Stability Analysis ◽  
Heat Equation ◽  
Numerical Experiments ◽  
Numerical Evaluation ◽  
Radiation Condition ◽  
Hankel Transform ◽  
Basis Functions ◽  
Infinite Cylinder ◽  
Stable Algorithm ◽  
Hankel Transforms

A new stable algorithm, based on hat functions for numerical evaluation of Hankel transform of order ν>-1, is proposed in this paper. The hat basis functions are used as a basis to expand a part of the integrand, rf(r), appearing in the Hankel transform integral. This leads to a very simple, efficient, and stable algorithm for the numerical evaluation of Hankel transform. The novelty of our paper is that we give error and stability analysis of the algorithm and corroborate our theoretical findings by various numerical experiments. Finally, an application of the proposed algorithm is given for solving the heat equation in an infinite cylinder with a radiation condition.

scholarly journals On the influence of basic thermodynamics on thermal cracking resistance of asphalt mixtures in cooling tests

2018 ◽  
Vol 3 ◽  
pp. 1-7
Author(s):  
Daniel Steiner ◽  
Bernhard Hofko
Keyword(s):  
Tensile Strength ◽  
Cooling Rate ◽  
Thermal Cracking ◽  
Radiation Condition ◽  
Asphalt Mixtures ◽  
Air Cooling ◽  
Laboratory Assessment ◽  
Cracking Resistance ◽  
Viscoelastic Parameters ◽  
The Impact

The cooling test or Thermal Stress Restrained Specimen Test (TSRST) simulates fully restrained pavements, as they occur in field for laboratory assessment of the thermal cracking resistance of asphalt mixtures. In the TSRST, cryogenic stress builds up due to cooling and prevented shrinkage until the tensile strength of the specimen is exceeded and the specimen fails by cracking. By carrying out TSRST various viscoelastic parameters, e.g. relaxation, evolution of tensile stresses, and tensile strength can be analyzed. Thus, a comprehensive view on the low temperature performance is possible. Standard TSRST is controlled by setting the cooling rate of the air within the chamber at a fixed value, e.g. -10°C/h. In thermodynamics, the actual cooling rate of objects is not only influenced by the cooling but also by external conditions like humidity, air velocity, radiation condition, etc. A current study investigates the impact of additional cooling parameters rather than just the air cooling rate. Two test machines of the same manufacturer that differ in the year of production and the setup of the climate chamber are compared. An initial wide scatter of test results from the two devices could be explained by taking thermodynamics into account and the reproducibility could be significantly enhanced.

scholarly journals Options for solving the problem of parts of the Shelter object located outside the New Safe Confinement

2020 ◽  
Vol 19 (4) ◽  
pp. 57-65
Author(s):  
O. V. Balan ◽  
◽  
S. Gh. Brylka ◽  
V. V. Derengovskyi ◽  
V. V. Yehorov ◽  
...  
Keyword(s):  
Cost Effective ◽  
Radiation Condition ◽  
Design Stage ◽  
Final Decision ◽  
Building Structures ◽  
Short Term ◽  
Design Studies ◽  
Financial Costs ◽  
Work Area ◽  
Goals And Objectives

The parts of the Shelter object structures remained outside the New Safe Confinement (protruding parts) are considered in the article. The analysis of the building structures condition of the turbine hall and the deaerator stack protruding parts on the east and west sides is carried out and the necessity of works on strengthening and/or dismantling of bearing structures is confirmed. Possible variants of reconstruction of the Shelter object protruding parts are stated and the technological sequence of works is provided. The analysis of the possibilities of performing works in the conditions of functioning of the New Safe Confinement — Shelter object system proved that such activity is rather difficult task, which can cause significant physical and financial costs. As there is no guarantee of trouble-free operation of the building structures of the protruding parts during the entire service life of the New Safe Confinement, it is necessary to make every effort to solve this problem in the short term. The results of the analysis allow to choose the most advantageous solution to the goals and objectives for the safest and most cost/effective dismantling and/or strengthening of structures of protruding parts, taking into account a number of different criteria. These criteria may be different in nature, which allowed to build a generalized efficiency indicator for individual criteria with certain weights that determine the importance of each of the criteria for decision making. Based on the results of the analysis, these options can be considered equivalent. The final decision on the choice of the optimal variant for the Shelter object protruding parts reconstruction can be made after detailing the technological decisions at the design stage of protruding parts reconstruction and before the design studies of the radiation condition in the work area. The obtained information can be used as input data during the design of the reconstruction of the deaerator stack and the turbine hall parts of the Shelter object, which protrude beyond the New Safe Confinement.

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