On the Simulation of Powered Axles Stick-Slip

2015 ◽  
Vol 809-810 ◽  
pp. 610-615
Author(s):  
Cristina Mihaela Tudorache ◽  
Razvan Andrei Oprea ◽  
Cornelia Stan
Keyword(s):  
Steady State ◽  
Frequency Domain ◽  
Time History ◽  
Dynamics Simulation ◽  
Negative Slope ◽  
Axial Vibration ◽  
Stick Slip ◽  
Validation And Verification ◽  
Friction Parameters ◽  
Reduced Scale

The use of high power railway vehicles requires enhanced control of wheel-rail adherence. When setting the train in motion, driving axles can exhibit torsional vibrations resulting in poor adherence and even axle damage. A significant number of railway authorities safety warnings and accident reports were issued related to the above phenomena. Adhesion saturation and negative slope are the characteristics which lead to self-sustained axial vibration. The aim of the present work is to prove the appropriateness of non-smooth models in the study of the axle torsional stick-slip vibrations which may occur when traction vehicles are set into motion. The model is simple, observes the main friction characteristics and provides the basis for efficient dynamics simulation. An experimental setup comprising a reduced scale wheel set is analyzed in order to validate the model proposed. The friction parameters are then identified using the proposed force-creepage relationship. Validation and verification is further carried out in frequency domain using both steady state and transient manoeuvres. Specific phenomena like discontinuities in the time-history friction force values occur. Validation and verification is carried out in frequency domain using both steady state and transient manoeuvres. From the comparison between the numerical and experimental results, it can be concluded that the setup is modeled accurately. Related problems may be solved using the present method, as it is pointed out in the article.

scholarly journals A Fast Frequency Domain Method for Steady-State Solution of Forced Vibration of System with Complex Damping

2020 ◽  
Vol 10 (10) ◽  
pp. 3442
Author(s):  
Wenrui Qi ◽  
Danguang Pan ◽  
Yongtao Gao ◽  
Wenyan Lu ◽  
Ying Huang
Keyword(s):  
Fourier Transform ◽  
Fourier Series ◽  
Steady State ◽  
Frequency Domain ◽  
Imaginary Part ◽  
Complete Solution ◽  
Time History ◽  
Frequency Domain Method ◽  
Domain Method ◽  
Complex Damping

The conventional frequency domain method (CFDM) and dual-force-based time domain method (DTDM) are often used to solve the steady-state response of system with complex damping under an arbitrary force. However, the calculation efficiency of the DTDM is low due to the straightforward summation operation of series even if the solution of the DTDM is the exact real part of the solution. In addition, since the CFDM only can obtain the real part of solution not the complete solution, it gives misleading information that the solution does not have an imaginary part. In this paper, a fast frequency domain method (FFDM) is proposed to calculate the complete response of complex damping system including the imaginary part with a higher accuracy in a much faster manner. The new FFDM uses half of the Fourier series of the discrete Fourier transform of the actual arbitrary force to construct the Fourier series of the dual force, followed by calculating the time history response using the inverse fast Fourier transform. The new developed method is validated through three numerical examples with harmonic and seismic excitations. The numerical results show that the accuracy of the new FFDM is compatible to the DTDM but with much higher computational efficiency.

Experimental Investigation of Power Umbilical Damping

2017 ◽  
Author(s):  
Torfinn Ottesen
Keyword(s):  
Steady State ◽  
Energy Input ◽  
State Energy ◽  
Seawater Temperature ◽  
Structural Damping ◽  
Stick Slip ◽  
Slip Regime ◽  
Free Decay ◽  
Vortex Induced Vibrations ◽  
Slip Transition

Ocean currents may cause vortex induced vibrations (VIV) of deep-water umbilicals and cables. Since the VIV response may give significant contributions to the total fatigue damage it is important to know the structural damping for relevant curvature levels. A laboratory test has been performed on a 12.5 m long test specimen to determine the damping for a range of curvature levels that are in the vicinity of the stick-slip transition region. The energy input to maintain steady state oscillations with curvature amplitudes in the range 0.0002–0.001 m−1 was measured. The steady state energy input is consistent with damping ratios obtained using the free decay method. The structural damping depends on construction temperature and curvature and is less for typically low seawater temperature and low curvatures. The transition between the stick- and the slip regime is seen for typical seawater temperature.

Motion in frequency domain for harmonic balance simulation of electrical machines

2018 ◽  
Vol 37 (4) ◽  
pp. 1449-1460
Author(s):  
Markus Wick ◽  
Sebastian Grabmaier ◽  
Matthias Juettner ◽  
Wolfgang Rucker
Keyword(s):  
Steady State ◽  
Frequency Domain ◽  
Efficient Method ◽  
Harmonic Balance ◽  
Eddy Currents ◽  
Computational Effort ◽  
Electrical Machines ◽  
Accurate Approximation ◽  
Content Type ◽  
Magnetic Devices

Purpose The high computational effort of steady-state simulations limits the optimization of electrical machines. Stationary solvers calculate a fast but less accurate approximation without eddy-currents and hysteresis losses. The harmonic balance approach is known for efficient and accurate simulations of magnetic devices in the frequency domain. But it lacks an efficient method for the motion of the geometry. Design/methodology/approach The high computational effort of steady-state simulations limits the optimization of electrical machines. Stationary solvers calculate a fast but less accurate approximation without eddy-currents and hysteresis losses. The harmonic balance approach is known for efficient and accurate simulations of magnetic devices in the frequency domain. But it lacks an efficient method for the motion of the geometry. Findings The three-phase symmetry reduces the simulated geometry to the sixth part of one pole. The motion transforms to a frequency offset in the angular Fourier series decomposition. The calculation overhead of the Fourier integrals is negligible. The air impedance approximation increases the accuracy and yields a convergence speed of three iterations per decade. Research limitations/implications Only linear materials and two-dimensional geometries are shown for clearness. Researchers are encouraged to adopt recent harmonic balance findings and to evaluate the performance and accuracy of both formulations for larger applications. Practical implications This method offers fast-frequency domain simulations in the optimization process of rotating machines and so an efficient way to treat time-dependent effects such as eddy-currents or voltage-driven coils. Originality/value This paper proposes a new, efficient and accurate method to simulate a rotating machine in the frequency domain.

scholarly journals The relevance of non-stationarities and non-Gaussianities in vibration fatigue

2018 ◽  
Vol 165 ◽  
pp. 10011 ◽  
Author(s):  
Martin Česnik ◽  
Janko Slavič ◽  
Lorenzo Capponi ◽  
Massimiliano Palmieri ◽  
Filippo Cianetti ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Dynamic Loading ◽  
Amplitude Modulation ◽  
Time History ◽  
Power Density Spectrum ◽  
Time To Failure ◽  
Density Spectrum ◽  
Frequency Domain Methods ◽  
Vibration Fatigue ◽  
Non Gaussian

In classical fatigue of materials, the frequency contents of dynamic loading are well below the natural frequencies of the observed structure or test specimen. However, when dealing with vibration fatigue the frequency contents of dynamic loading and structure's dynamic response overlap, resulting in amplified stress loads of the structure. For such cases, frequency counting methods are especially convenient. Gaussianity and stationarity assumptions are applied in frequency-domain methods for obtaining dynamic structure's response and frequency-domain methods for calculating damage accumulation rate. Since it is common in real environments for the structure to be excited with non-Gaussian and non-stationary loads, this study addresses the effects of such dynamic excitation to experimental time-to-failure of a structure. Initially, the influence of non-Gaussian stationary excitation is experimentally studied via excitation signals with equal power density spectrum and different values of kurtosis. Since no relevant changes of structure's time-to-failure were observed, the study focused on non-stationary excitation signals that are also inherently non-Gaussian. The non-stationarity of excitation was achieved by amplitude modulation and significantly shorter times-to-failure were observed when compared to experiments with stationary non-Gaussian excitation. Additionally, the structure's time-to-failure varied with the rate of the amplitude modulation. To oversee this phenomenon the presented study proposes a non-stationarity index which can be obtained from the excitation time history. The non-stationarity index was experimentally confirmed as a reliable estimator for severity of non-stationary excitation. The non-stationarity index is used to determine if the frequencydomain methods can safely be applied for time-to-failure calculation.

Determination of Pressure Profile During Closed-Vessel Test Through Computational Fluid Dynamics Simulation

2015 ◽  
Vol 8 (2) ◽  
Author(s):  
Ahmed Bougamra ◽  
Huilin Lu
Keyword(s):  
Solid Propellant ◽  
Time History ◽  
Initial Pressure ◽  
Pressure Profile ◽  
Dynamics Simulation ◽  
Solid Propellants ◽  
Closed Vessel ◽  
Governing Equations ◽  
Two Phase ◽  
Closed Chamber

Two-phase flow modeling of solid propellants has great potential for simulating and predicting the ballistic parameters in closed-vessel tests as well as in guns. This paper presents a numerical model describing the combustion of a solid propellant in a closed chamber and takes into account what happens in such two-phase, unsteady, reactive-flow systems. The governing equations were derived in the form of coupled, nonlinear axisymmetric partial differential equations. The governing equations with customized parameters were implemented into ansys fluent 14.5. The presented solutions predict the pressure profile inside the closed chamber. The results show that the present code adequately predicts the pressure–time history. The numerical results are in agreement with the experiment. Some discussions are given regarding the effect of the grain shape and the sensitivity of these predictions to the initial pressure of the solid propellant bed. The study demonstrated the capability of using the present model implemented into Fluent, to simulate the combustion of solid propellants in a closed vessel and, eventually, the interior ballistic process in guns.

Sign in / Sign up

Export Citation Format

Share Document