scholarly journals Modeling transient vibration-sound generation processes

2020 ◽  
pp. 39-42
Author(s):  
Petro Volodymyrovich Lukianov
Keyword(s):  
Comparative Analysis ◽  
Mach Number ◽  
Sound Field ◽  
Numerical Results ◽  
Sound Generation ◽  
Transient Vibration ◽  
Helicopter Landing ◽  
Blade Flutter ◽  
Sinusoidal Shape ◽  
Transitional Mode

In this paper, a problem of sound generation of two-blade rotor sinusoidal shape during helicopter landing is solved. Near and far sound field characteristics have been calculated. A comparative analysis of obtained numerical results with results for Mach number 0.2<M<0.4 is given. In particular noticed, that for a low Mach’s number M<0.1 transitional mode can occurs, which produces a blade flutter as a result.

An Assessment of Five Turbulence Models in Predicting Turbulent Separation

2004 ◽  
Author(s):  
Robert E. Spall ◽  
Warren F. Phillips ◽  
Nick Alley
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Mach Number ◽  
Turbulence Models ◽  
Streamwise Velocity ◽  
Numerical Results ◽  
Flow Conditions ◽  
Turbulent Separation ◽  
Controlled Flow ◽  
Flow Case

Four different turbulence models were employed to predict the flow over a wall-mounted Glauert-Goldschmied body. The models evaluated include: 1) two-layer k–ε, 2) shear stress transport, 3) low-Reynolds number k–ω, 4) Spalart-Allmaras, and 5) v2−f. Calculations were performed for both an uncontrolled case, and a controlled-flow case which used steady suction through a slot located at the 65% chord station. The flow conditions include a freestream Mach number of approximately 0.1, and a chord Reynolds number of just under 1 million. For each model, the numerical results over predicted the experimentally determined re-attachment length. An examination of streamwise velocity profiles at several stations downstream of the trailing edge revealed considerable variation in the predictions of the five turbulence models.

On unsteady surface forces, and sound produced by the normal chopping of a rectilinear vortex

1989 ◽  
Vol 206 ◽  
pp. 131-153 ◽  
Author(s):  
M. S. Howe
Keyword(s):  
Mach Number ◽  
General Formula ◽  
Small Angle ◽  
Related Problem ◽  
Median Plane ◽  
Surface Forces ◽  
Numerical Results ◽  
Acoustic Source ◽  
Dipole Strength ◽  
Low Mach Number

An investigation is made of the sound produced when a rectilinear vortex is cut at right angles to its axis by a non-lifting airfoil of symmetric section. The motions are at sufficiently low Mach number that the wavelength of the sound is large relative to the chord of the airfoil. In these circumstances the airfoil experiences no fluctuating lift during the interaction, and the radiation may be ascribed to an acoustic source of dipole type whose strength is equal to the unsteady drag. It is argued that previous analyses of the related problem of ‘unsteady thickness noise’ have ignored certain terms whose inclusion greatly reduces the predicted intensity of the radiation. A general formula for the surface forces (derived in an appendix) is applied to deduce that the dipole strength is proportional to the square of the circulation of the vortex, and depends on the spanwise acceleration of the vortex induced by images in the airfoil. Numerical results are presented for typical airfoil sections, and a comparison is made with the unsteady lifting noise generated when the axis of the vortex is inclined at a small angle to the normal to the median plane of the airfoil.

CVA UNDER ALTERNATIVE SETTLEMENT CONVENTIONS AND WITH SYSTEMIC RISK

2013 ◽  
Vol 16 (07) ◽  
pp. 1350039 ◽  
Author(s):  
CYRIL DURAND ◽  
MAREK RUTKOWSKI
Keyword(s):  
Comparative Analysis ◽  
Systemic Risk ◽  
General Framework ◽  
Practical Importance ◽  
Numerical Results ◽  
Counterparty Risk ◽  
Market Environment ◽  
Financial Contracts

We propose a fairly general framework which allows one to perform Credit Value Adjustment (CVA) computations for a contract with bilateral counterparty risk in the presence of (a) systemic risk and (b) wrong-way or right-way risks. Our methodology focuses on the role of alternative settlement clauses, but it also aims to cover various features of margin agreements. We present a comparative analysis of numerical results that supports our initial conjecture that alternative specifications of settlement values have a nonnegligible impact on CVA computations for contracts with bilateral counterparty risk. Our conclusions emphasize the practical importance of more sophisticated models that are capable of fully reflecting the actual features of financial contracts, as well as the influence of the market environment.

On sound generated aerodynamically I. General theory

1952 ◽  
Vol 211 (1107) ◽  
pp. 564-587 ◽  
Keyword(s):  
Fluid Flow ◽  
Mach Number ◽  
General Theory ◽  
Stress Tensor ◽  
High Power ◽  
Velocity Vector ◽  
Unit Volume ◽  
Equations Of Motion ◽  
Sound Field ◽  
Velocity Of Sound

A theory is initiated, based on the equations of motion of a gas, for the purpose of estimating the sound radiated from a fluid flow, with rigid boundaries, which as a result of instability contains regular fluctuations or turbulence. The sound field is that which would be produced by a static distribution of acoustic quadrupoles whose instantaneous strength per unit volume is ρv i v j + p ij - a 2 0 ρ δ ij , where ρ is the density, v i the velocity vector, p ij the compressive stress tensor, and a 0 the velocity of sound outside the flow. This quadrupole strength density may be approximated in many cases as ρ 0 v i v j . The radiation field is deduced by means of retarded potential solutions. In it, the intensity depends crucially on the frequency as well as on the strength of the quadrupoles, and as a result increases in proportion to a high power, near the eighth, of a typical velocity U in the flow. Physically, the mechanism of conversion of energy from kinetic to acoustic is based on fluctuations in the flow of momentum across fixed surfaces, and it is explained in § 2 how this accounts both for the relative inefficiency of the process and for the increase of efficiency with U . It is shown in § 7 how the efficiency is also increased, particularly for the sound emitted forwards, in the case of fluctuations convected at a not negligible Mach number.

scholarly journals The stability of a trailing-line vortex in compressible flow

1994 ◽  
Vol 269 ◽  
pp. 323-351 ◽  
Author(s):  
Jillian A. K. Stott ◽  
Peter W. Duck
Keyword(s):  
Mach Number ◽  
Compressible Flow ◽  
Numerical Results ◽  
Line Vortex ◽  
Mach Numbers ◽  
The Stability ◽  
Vortex Axis ◽  
Very High ◽  
High Wavenumbers

We consider the inviscid stability of the Batchelor (1964) vortex in a compressible flow. The problem is tackled numerically and also asymptotically, in the limit of large (azimuthal and streamwise) wavenumbers, together with large Mach numbers. The nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumbers. At very high wavenumbers and Mach numbers, the mode which is present in the incompressible case ceases to be unstable, whilst a new ‘centre mode’ forms, whose stability characteristics are determined primarily by conditions close to the vortex axis. We find that generally the flow becomes less unstable as the Mach number increases, and that the regime of instability appears generally confined to disturbances in a direction counter to the direction of the rotation of the swirl of the vortex.Throughout the paper comparison is made between our numerical results and results obtained from the various asymptotic theories.

scholarly journals Investigation of the effects of main geometric parameters and flow characteristics on secondary flow losses in a turbine cascade

2021 ◽  
Vol 2131 (3) ◽  
pp. 032081
Author(s):  
M Mesbah ◽  
V G Gribin ◽  
K Souri
Keyword(s):  
Mach Number ◽  
Aspect Ratio ◽  
Total Energy ◽  
Flow Characteristics ◽  
Numerical Results ◽  
Energy Losses ◽  
Inlet Flow ◽  
Flow Angle ◽  
Flow Losses ◽  
Exit Mach Number

Abstract This paper presents numerical simulation results of a three-dimensional (3D) transitional flow in a stator cascade of an axial turbine. The influences of the main geometric parameters and flow characteristics including, the blade aspect ratio, pitch-to-chord ratio, inlet flow angle, and exit Mach number, on secondary flows development and end-wall losses, were studied. The numerical results were validated by the results of experiments conducted in the laboratory of the steam and gas turbine faculty of the Moscow Power Engineering Institute. The maximum difference between computed and experimental results was 2.4 %. The total energy losses decrease by 20 % when the exit Mach number changes from 0.38 to 0.8. Numerical results indicated that the blade aspect ratio had the most effect on secondary flow losses. The total energy losses increase by 46.6 % when the aspect ratio decreases from 1 to 0.25. The total loss of energy by 13.2 % decreases by increasing the inlet flow angle from 60 degrees to 90 degrees. Then by increasing the inlet flow angle from 90 to 110 degrees, the total loss rises by 3.6%. As the pitch-to-chord ratio increases from 0.7 to 0.75, the total energy losses are reduced by 12.2 %. Then by increasing the pitch-to-chord ratio from 0.75 to 0.8, the total energy losses increase by 6 %. As with experimental data, the numerical results showed that the optimal inlet flow angle and relative pitch for the cascade are 90 degrees and 0.75, respectively.

scholarly journals A Comparative Analysis of Monte Carlo and Quasi-Monte Carlo Methods in Financial Derivative Pricing

2021 ◽  
Vol 69 (1) ◽  
pp. 1-6
Author(s):  
SM Arif Hossen ◽  
ABM Shahadat Hossain
Keyword(s):  
Monte Carlo ◽  
Comparative Analysis ◽  
Monte Carlo Methods ◽  
American Options ◽  
Financial Derivatives ◽  
Numerical Results ◽  
Derivative Pricing ◽  
Quasi Monte Carlo ◽  
Financial Derivative ◽  
Path Dependent

The main purpose of this dissertation is to study Monte Carlo (MC) and Quasi-Monte Carlo (QMC) methods for pricing financial derivatives. We estimate the Price of European as well as various path dependent options like Asian, Barrier and American options by using these methods. We also compute the numerical results by the above mentioned methods and compare them graphically as well with the help of the MATLAB Coding. Dhaka Univ. J. Sci. 69(1): 1-6, 2021 (January)

COMPARATIVE ANALYSIS BY MEANS OF FINITE DIFFERENCES AND DM METHODS FOR LINEARIZED PROBLEM OF GYROTRONS

2005 ◽  
Vol 9 (2) ◽  
pp. 127-136
Author(s):  
T. Cirulis ◽  
H. Kalis ◽  
O. Lietuvietis
Keyword(s):  
Comparative Analysis ◽  
Schrödinger Equation ◽  
Boundary Conditions ◽  
Finite Differences ◽  
Schrodinger Equation ◽  
Numerical Results ◽  
Linearized Problem ◽  
Complex Boundary ◽  
Fast Oscillations

The problem of Schrödinger equation with complex boundary conditions for modelling a motion of electrons in gyrotrons is considered. Numerical results obtained by using Fourier, Finite Differences (FD) and Degenerate Matrices (DM) methods are compared in the simplest case. For DM methods they are analysed also in more general cases, when FD can not be applied because of fast oscillations of the solution. Santrauka Nagrinejamas kraštinis uždavinys Šredingerio lygčiai, aprašantis elektronu judejima girotrone. Darbe lyginami ir analizuojami Furje, baigtiniu skirtumu ir degeneruotu matricu (DM) metodais gauti skaitiniai rezultatai. Aptartas metodo taikymas greitu osciliaciju atveju.

Comprehensive Array Measurements of In-Car Sound Field in Magnitude and Phase for Active Sound Generation and Noise Control

2014 ◽  
Vol 7 (2) ◽  
pp. 596-602 ◽  
Author(s):  
Matthias Frank ◽  
Franz Zotter ◽  
Alois Sontacchi ◽  
Stephan Brandl ◽  
Christian Kranzler
Keyword(s):  
Noise Control ◽  
Sound Field ◽  
Sound Generation ◽  
Array Measurements
Sign in / Sign up

Export Citation Format

Share Document