scholarly journals An Efficient Approach for Predicting Resonant Response with the Utilization of the Time Transformation Method and the Harmonic Forced Response Method

Aerospace ◽  
2021 ◽  
Vol 8 (11) ◽  
pp. 312
Author(s):  
Xiaojie Zhang ◽  
Yanrong Wang ◽  
Xianghua Jiang
Keyword(s):  
Computing Time ◽  
Transformation Method ◽  
Forced Response ◽  
Time Transformation ◽  
Resonant Response ◽  
Efficient Approach ◽  
Mean Pressure ◽  
Time Required ◽  
Response Method ◽  
Dangerousness Assessment

Resonant response of turbomachinery blades can lead to high cycle fatigue (HCF) if the vibration amplitudes are significant. Therefore, the dangerousness assessment of the resonance crossing is important. It requires accurate predictions of the aerodynamic excitation, damping, and response, which will consume immense computational costs. The novel aspect of this study is the development of an efficient approach, which incorporates the time transformation (TT) method to predict the aerodynamic excitations and the harmonic forced response method to obtain the response levels. The efficiency and accuracy of this method were evaluated by comparing with traditional methods for the resonance crossing excited by upstream wake in a 1.5 multistage compressor. For the aerodynamic excitation, discrepancies of 2% at the mean pressure and 25% at the harmonic pressure in most areas expect for the blade root were observed, but the calculation time required by the TT method was only 5% of that by the time-marching method. Moreover, response levels with the same aerodynamic forces were compared between the harmonic forced-response and transient dynamic methods. Small differences in the displacement and stress variables were observed; the relative deviation was smaller than 2% with only 1% computing time compared with the transient method, indicating the high accuracy and efficiency of the efficient approach.

scholarly journals Closed-Form Expressions for Numerical Evaluation of Self-Impedance Terms Involved on Wire Antenna Analysis by the Method of Moments

Electronics ◽  
2021 ◽  
Vol 10 (11) ◽  
pp. 1316
Author(s):  
Carlos-Ivan Paez-Rueda ◽  
Arturo Fajardo ◽  
Manuel Pérez ◽  
Gabriel Perilla
Keyword(s):  
Numerical Integration ◽  
Method Of Moments ◽  
Computing Time ◽  
Basis Functions ◽  
Wire Antenna ◽  
Complex Geometries ◽  
Point Matching ◽  
Piecewise Constant ◽  
Matching Procedure ◽  
Time Required

This paper proposes new closed expressions of self-impedance using the Method of Moments with the Point Matching Procedure and piecewise constant and linear basis functions in different configurations, which allow saving computing time for the solution of wire antennas with complex geometries. The new expressions have complexity O(1) with well-defined theoretical bound errors. They were compared with an adaptive numerical integration. We obtain an accuracy between 7 and 16 digits depending on the chosen basis function and segmentation used. Besides, the computing time involved in the calculation of the self-impedance terms was evaluated and compared with the time required by the adaptative quadrature integration solution of the same problem. Expressions have a run-time bounded between 50 and 200 times faster than an adaptive numerical integration assuming full computation of all constant of the expressions.

SnBversion 2.2: an example of crystallographic multiprocessing

2002 ◽  
Vol 35 (3) ◽  
pp. 374-376 ◽  
Author(s):  
Jason Rappleye ◽  
Martins Innus ◽  
Charles M. Weeks ◽  
Russ Miller
Keyword(s):  
Shared Memory ◽  
Distributed Memory ◽  
Computing Time ◽  
Direct Methods ◽  
Fixed Number ◽  
Linear Speedup ◽  
Beowulf Clusters ◽  
Shared Memory Multiprocessor ◽  
Computing Platforms ◽  
Time Required

The computer programSnBimplements a direct-methods algorithm, known asShake-and-Bake, which optimizes trial structures consisting of randomly positioned atoms. Although largeShake-and-Bakeapplications require significant amounts of computing time, the algorithm can be easily implemented in parallel in order to decrease the real time required to achieve a solution. By using a master–worker model,SnBversion 2.2 is amenable to all of the prevalent modern parallel-computing platforms, including (i) shared-memory multiprocessor machines, such as the SGI Origin2000, (ii) distributed-memory multiprocessor machines, such as the IBM SP, and (iii) collections of workstations, including Beowulf clusters. A linear speedup in the processing of a fixed number of trial structures can be obtained on each of these platforms.

Exact Response of a Translating String With Arbitrarily Varying Length Under General Excitation

2008 ◽  
Vol 75 (3) ◽  
Author(s):  
W. D. Zhu ◽  
N. A. Zheng
Keyword(s):  
Boundary Conditions ◽  
Initial Conditions ◽  
Control Volume ◽  
Parametric Instability ◽  
Transformation Method ◽  
Forced Response ◽  
Rate Of Change ◽  
Solution Methods ◽  
Vibrating String ◽  
Varying Length

The exact response of a translating string with constant tension and arbitrarily varying length is determined under general initial conditions and external excitation. The governing equation is transformed to a standard hyperbolic equation using characteristic transformation. The domain of interest for the transformed equation is divided into groups of subdomains according to the properties of wave propagation. d’Alembert’s solution for any point in the zeroth subdomain group is obtained by using the initial conditions. The solution is extended to the whole domain of interest by using the boundary conditions, and a recursive mapping is found for the solution in the second and higher groups of subdomains. The least upper bound of the displacement of the freely vibrating string is obtained for an arbitrary movement profile. The forced response of the string with nonhomogeneous boundary conditions is obtained using a transformation method and the direct wave method. A new method is used to derive the rate of change of the vibratory energy of the translating string from the system viewpoint. Three different approaches are used to derive and interpret the rate of change of the vibratory energy of the string within a control volume, and the energy growth mechanism of the string during retraction is elucidated. The solution methods are applied to a moving elevator cable with variable length. An interesting parametric instability phenomenon in a translating string with sinusoidally varying length is discovered.

The Interaction Between Mistuning and Friction in the Forced Response of Bladed Disk Assemblies

1985 ◽  
Vol 107 (1) ◽  
pp. 205-211 ◽  
Author(s):  
J. H. Griffin ◽  
A. Sinha
Keyword(s):  
Gas Turbine ◽  
Turbine Blades ◽  
Forced Response ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Resonant Response ◽  
Friction Dampers ◽  
Bladed Disk ◽  
The Impact ◽  
Slip Force

This paper summarizes the results of an investigation to establish the impact of mistuning on the performance and design of blade-to-blade friction dampers of the type used to control the resonant response of turbine blades in gas turbine engines. In addition, it discusses the importance of friction slip force variations on the dynamic response of shrouded fan blades.

scholarly journals FRACS: modelling of the dust disc of the B[e] CPD-57° 2874 from VLTI/MIDI data

2010 ◽  
Vol 6 (S272) ◽  
pp. 382-383
Author(s):  
Philippe Bendjoya ◽  
Armando Domiciano de Souza ◽  
Gilles Niccolini
Keyword(s):  
Computing Time ◽  
Mid Infrared ◽  
Fitting Procedure ◽  
Dust Temperature ◽  
Tracing Algorithm ◽  
Short Computing Time ◽  
Time Required ◽  
Best Fit ◽  
Physical Quantities ◽  
Automatic Fitting

AbstractThe physical interpretation of spectro-interferometric data is strongly model dependent. On one hand, models involving elaborate radiative transfer solvers are in general too time consuming to perform an automatic fitting procedure and derive astrophysical quantities and their related errors. On the other hand, using simple geometrical models does not give sufficient insights into the physics of the object. We developed a numerical tool optimised for mid-infrared (mid-IR) interferometry, the Fast Ray-tracing Algorithm for Circumstellar Structures (FRACS). Thanks to the short computing time required by FRACS, best-fit parameters and uncertainties for several physical quantities were obtained, such as inner dust radius, relative flux contribution of the central source and of the dusty CSE, dust temperature profile, disc inclination.

Modal and Aeroelastic Analysis of a Compressor Blisk Considering Mistuning

2011 ◽  
Author(s):  
Jens Nipkau ◽  
Arnold Ku¨hhorn ◽  
Bernd Beirow
Keyword(s):  
Equations Of Motion ◽  
Computing Time ◽  
Element Model ◽  
Forced Response ◽  
Lumped Mass ◽  
Aerodynamic Forces ◽  
Mass Model ◽  
Influence Coefficients ◽  
Aeroelastic Analysis ◽  
Lumped Mass Model

Focussing on three basic blade modes the effect of the flow’s influence on the forced response of a mistuned HPC-blisk is studied using a surrogate lumped mass model called equivalent blisk model (EBM). Both measured and intentionally allowed mistuning is considered to find out in principle if the flow contributes to a slowdown of blade displacements with increasing mistuning. In a first step the mechanical properties of the EBM are adjusted to a finite element model and known mistuning distributions given in terms of blade frequencies and damping. Taking into account the flow structure interaction CFD-computations are carried out in order to derive aerodynamic influence coefficients (AIC) which are used to describe the aerodynamic forces coming along with the motion of each blade in the flow. These aerodynamic forces can be included directly in the EBM equations of motion or alternatively be used to calculate aeroelastic eigenvalues from which additional equivalent aerodynamic elements representing the co-vibrating air mass as well as aerodynamic stiffening and damping effects are derived. Both kinds of EBM are applied to study the forced response at least in a qualitative manner aiming to demonstrate some basic effects at low computing time.

Preprocessing of Coefficients for Reusable Continuous Wavelet Transform

2014 ◽  
Vol 1040 ◽  
pp. 975-979 ◽  
Author(s):  
Alexander A. Khamukhin ◽  
Alexey A. Khamukhin
Keyword(s):  
Wavelet Transform ◽  
Continuous Wavelet Transform ◽  
Computing Time ◽  
Continuous Wavelet ◽  
Wavelet Coefficients ◽  
Nonstationary Signal ◽  
Online Detection ◽  
Second Stage ◽  
Time Required ◽  
Two Stages

The division into two stages of the Continuous Wavelet Transform (CWT) computing is proposed. This is expedient in circumstances when CWT is repeated many times, e.g., for online detection of nonstationary signal singularities. It is shown that the preprocessing of wavelet coefficients in the first stage can significantly reduce computing time required in the second stage. The comparative estimation of the runtime reduction in the second stage of CWT calculation is deduced.

Experimental Reduction of Transonic Fan Forced Response by IGV Flow Control

2004 ◽  
Author(s):  
S. Todd Bailie ◽  
Wing F. Ng ◽  
William W. Copenhaver
Keyword(s):  
Flow Control ◽  
Forced Response ◽  
Resonant Response ◽  
Compressor Blades ◽  
Resonant Amplitude ◽  
Engine Order ◽  
Blade Vibrations ◽  
Fan Blade ◽  
Transonic Fan ◽  
Bending Response

The main contributor to the high-cycle fatigue of compressor blades is the response to aerodynamic forcing functions generated by an upstream row of stators or inlet guide vanes. Resonant response to engine order excitation at certain rotor speeds can be especially damaging. Studies have shown that flow control by trailing edge blowing (TEB) can reduce stator wake strength and the amplitude of the downstream rotor blade vibrations generated by the unsteady stator-rotor interaction. In the present study, the effectiveness of TEB to reduce forced fan blade vibrations was evaluated in a modern single-stage transonic fan rig. Data was collected for multiple uniform full-span TEB conditions over a range of rotor speed including multiple modal resonance crossings. Resonant response sensitivity was generally characterized by a robust region of strong attenuation. The baseline resonant amplitude of the first torsion mode, which exceeded the endurance limit on the critical blade, was reduced by more than 80% with TEB at 1.0% of the total rig flow. The technique was also found to be modally robust; similar reductions were achieved for all tested modal crossings, including more than 90% reduction of the second LE bending response using 0.7% of the rig flow.

Development of State of the Art Dynamic Stress Prediction Methodology for Steam Turbines

2011 ◽  
Author(s):  
Tie Chen ◽  
John Rogerson ◽  
Fang Yang ◽  
Gurnam Singh ◽  
Phil Hemsley
Keyword(s):  
Frequency Shift ◽  
Natural Frequency ◽  
Coupling Effect ◽  
Computing Time ◽  
Turbine Blades ◽  
Nonlinear Damping ◽  
Forced Response ◽  
Explicit Method ◽  
Friction Forces ◽  
Peak Response

To predict the dynamic stresses due to forced response of steam turbine blades, a commercial FE solver ABAQUS has been linked with an in-house CFD solver TF3D-VIB, in the time domain in both one-way and two-way coupling. Both methods have been applied to analyse a freestanding subsonic turbine stage excited by upstream flow perturbations. Over a frequency range the peak responses are very similar, but the peak response of two-way coupling is shifted to a lower frequency, due to the aerodynamic coupling effect of fluid-structure interaction. That means a speed / frequency sweep is necessary to search for the peak response in two-way coupling. However, in one-way coupling, the frequency shift can be derived from the vibration induced modal force, and only one calculation is needed to predict the response over a range of frequency ratio using the classic single degree-of-freedom equation. One calculation using two-way coupling typically takes seven times more computing time than one-way coupling. The total computing time for two-way coupling to define the response characteristic is therefore much higher; more calculations are needed and each calculation takes much longer. Thus a one-way coupling method including the frequency shift correction is much more practical and suitable for blade design iterations. The blade forced response is also limited by damping. In the case of low damping such as material only damping, this can be well represented in the harmonic ABAQUS calculation. However, high values of nonlinear damping can be deliberately introduced by managing the friction forces at blade root attachment. The nonlinear damping can be simulated directly by ABAQUS/Explicit method, convergence criteria often lead to excessive runtimes. Therefore a simple mass/spring model has been developed, which applies an exciting force to a system comprising two masses and springs to represent the blade and the root respectively and includes modelling of both the stick and slip forces of the root due to friction. Both the masses and their spring stiffness are chosen to produce either the sticking natural frequency (with infinite friction) or sliding natural frequency (zero friction). Using the simple two-mass model, the significant nonlinear response pattern is demonstrated. The resulting pattern has been verified against the ABAQUS/Explicit method. This allows the blade forced response prediction from the one way coupling to be further corrected to account for the nonlinear friction damping effect.

Reliability-based design optimization for vertical vibrations of a modified electric vehicle using fourth-moment polynomial standard transformation method

2020 ◽  
Vol 234 (10-11) ◽  
pp. 2649-2664
Author(s):  
Sheng Wang ◽  
Lin Hua ◽  
Xinghui Han ◽  
Zhuoyu Su
Keyword(s):  
Design Optimization ◽  
Electric Vehicle ◽  
Optimization Problems ◽  
Computing Time ◽  
Optimization Procedure ◽  
Transformation Method ◽  
Vertical Vibration ◽  
Fourth Moment ◽  
Reliability Based Design Optimization ◽  
Reliability Based Design

This article presents a new reliability-based design optimization procedure for the vertical vibration issues raised by a modified electric vehicle using fourth-moment polynomial standard transformation method. First, the fourth-moment polynomial standard transformation method with polynomial chaos expansion is used to obtain the reliability index of uncertain constraints in the reliability-based design optimization which is highly precise and saves computing time compared with other common methods. Next, the half-car model with nonlinear suspension parameters for the modified electric vehicle is investigated, and the response surface methodology is adopted to approximate the complex and time-consuming vertical vibration calculation to the polynomial expressions, and the approximation is validated for reliability-based design optimization results within permissible error level. Then, reliability-based design optimization results under both deterministic and uncertain load parameters are shown and analyzed. Unlike the traditional vertical vibration optimization that only considers one or several sets of load parameters, which lacks versatility, this article presents the reliability-based design optimization with uncertain load parameters which is more suitable for engineering. The results show that the proposed reliability-based design optimization procedure is an effective and efficient way to solve vertical vibration optimization problems for the modified electric vehicle, and the optimization statistics, including the maximum probability interval, can provide references for other suspension dynamical optimization.

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