1,721,101 research outputs found
On the formulation of the planar ANCF triangular finite elements
No full textIn this paper, new planar isoparametric triangular finite elements (FE) based on the absolute nodal coordinate formulation (ANCF) are developed. The proposed ANCF elements have six coordinates per node: two position coordinates that define the absolute position vector of the node and four gradient coordinates that define vectors tangent to coordinate lines (parameters) at the same node. To shed light on the importance of the element geometry and to facilitate the development of some of the new elements presented in this paper, two different parametric definitions of the gradient vectors are used. The first parametrization, called area parameterization, is based on coordinate lines along the sides of the element in the reference configuration, while the second parameterization, called Cartesian parameterization, employs coordinate lines defined along the axes of the structure (body) coordinate system. The fundamental differences between the ANCF parameterizations used in this investigation and the parametrizations used for conventional finite elements are highlighted. The Cartesian parameterization serves as a unique standard for the triangular FE assembly. To this end, a transformation matrix that defines the relationship between the area and the Cartesian parameterizations is introduced for each element in order to allow for the use of standard FE assembly procedure and define the structure (body) inertia and elastic forces. Using Bezier geometry and a linear mapping, cubic displacement fields of the new ANCF triangular elements are systematically developed. Specifically, two new ANCF triangular finite elements are developed in this investigation, namely four-node mixed-coordinate and three-node ANCF triangles. The performance of the proposed new ANCF elements is evaluated by comparison with the conventional linear and quadratic triangular elements as well as previously developed ANCF rectangular and triangular elements. The results obtained in this investigation show that in the case of small and large deformations as well as finite rotations, all the elements considered can produce correct results, which are in a good agreement if appropriate mesh sizes are used
Development of ANCF tetrahedral finite elements for the nonlinear dynamics of flexible structures
No full textIn this paper, methods for developing isoparametric tetrahedral finite elements (FE) based on the absolute nodal coordinate formulation (ANCF) are presented. The proposed ANCF tetrahedral elements have twelve coordinates per node that include three position and nine gradient coordinates. The fundamental differences between the coordinate parametrizations used for conventional finite elements and the coordinate parametrizations employed for the proposed ANCF tetrahedral elements are discussed. Two different parametric definitions are introduced: a volume parametrization based on coordinate lines along the sides of the tetrahedral element in the straight (undeformed) configuration and a Cartesian parametrization based on coordinate lines directed along the global axes. The volume parametrization facilitates the development of a concise set of shape functions in a closed form, and the Cartesian parametrization serves as a unique standard for the element assembly. A linear mapping based on the Bezier geometry is used to systematically define the cubic position fields of ANCF tetrahedral elements: the complete polynomial-based eight-node mixed-coordinate and the incomplete polynomial-based four-node ANCF tetrahedral elements. An element transformation matrix that defines the relationship between the volume and Cartesian parametrizations is developed and used to convert the parametric gradients to structure gradients, thereby allowing for the use of a standard FE assembly procedure. A general computational approach is employed to formulate the generalized inertia, external, and elastic forces. The performance of the proposed ANCF tetrahedral elements is evaluated by comparison with the conventional linear and quadratic tetrahedral elements and also with the ANCF brick element. In the case of small deformations, the numerical results obtained show that all the tetrahedral elements considered can correctly produce rigid body motion. In the case of large deformations, on the other hand, the solutions of all the elements considered are in good agreement, provided that appropriate mesh sizes are used
Analytical study and control of high-speed vehicle hunting stability with traction/braking torque
No full textThe lateral dynamics of railway vehicles are significantly influenced by traction and braking forces, primarily due to the saturation effects inherent in wheel-rail creep. This study establishes a dynamic modelling approach for railway wheelsets subject to traction and braking torques. It unravels the impacts of these forces on the stability of lateral oscillations, commonly known as hunting stability. An analytical method is employed to investigate the influence of traction and braking torque on the critical velocity required to maintain the stability of hunting motion. The results demonstrate the beneficial effects of traction and braking torque in enhancing hunting stability. Subsequently, an innovative strategy is proposed for maintaining the stability of hunting motion in high-speed vehicles. This involves applying traction and braking torque separately to the front and rear wheelsets of each bogie. The proposed method is then applied to a high-speed vehicle experiencing strong lateral vibrations under unstable conditions. The findings affirm the efficacy and safety of controlling hunting stability through interventions of traction and braking forces. This approach proves effective in mitigating abnormal vibrations arising from hunting instability in high-speed vehicles
On-board identification of wheel polygonization of metro trains based on convolutional neural network regression analysis and angular-domain synchronous averaging
No full textWheel polygonization, a form of wheel out-of-roundness, has become a common problem on trains of urban rail transit systems in recent years. It results in a significant increase of the dynamic responses of both the vehicle and the track, high vibration and noise levels, and structural fatigue. This paper proposes an innovative method for identifying wheel polygonization orders and their effective values using convolutional neural network (CNN) regression analysis. First, the acceleration signal measured on the axle box has been processed with the angular-domain synchronous averaging (ADSA) method, effectively separating the characteristic information associated with wheel polygonization within the signal. To extract comprehensive wheel polygonization information, a feature fusion method is employed, integrating features from both the time and frequency domain. Then, a CNN regression model is established and trained, with validation conducted using measured data of vehicle vibration and the wheel polygonization measured during field tests. Comparative analysis with different identification methods is performed, including a comparison of different preprocessing methods and machine learning models, which demonstrates the effectiveness of the proposed method in this study. The verification results show that the proposed method achieves high identification accuracy for wheel polygonization up to the 25th order. The overall average root mean square error value is 2.0 dB. Finally, the influence of wheel polygonization conditions, track stiffness, and speed fluctuation on the identification accuracy is discussed. The results show the proposed method exhibits robust identification capacity under varying conditions, which indicates its wide application and accuracy in complex situations during train service. This research contributes to advancing the field of wheel polygonization detection, offering a reliable and effective solution for application in railway systems
A DPIM-based probability analysis framework to obtain railway vehicle vibration characteristics considering the randomness of OOR wheel
No full textThe OOR (out-of-roundness) wheel is one of the main excitation sources causing vehicle vibration. However, the OOR wheel occurs randomly, indicating that the vibration behavior of a vehicle cannot be comprehensively evaluated using a deterministic approach. Thus, a probability analysis framework is proposed to obtain vehicle vibration characteristics while considering the randomness of the OOR wheel. The probability model of the random OOR wheel is derived by reducing the high-dimensional variables into a few independent variables of the radius, amplitude, and phase. Then, the vertical vehicle-track coupled system with OOR wheels is modelled. A DPIM (direct probability integral method) is further developed to analyze the evolution of excitation to response probabilities. Finally, the statistics of the random vibration of the vehicle are calculated. The proposed framework is verified using a numerical case. Results show that the PDF (probability density function) shape of the vehicle random vibration, induced by the Gaussian-distributed OOR wheel, deviates from the Gaussian distribution due to the nonlinear wheel/rail contact force. Instead, it exhibits a right-skewed shape, significantly impacting the dynamic performance. As the mean or coefficient of variation of the OOR wheel amplitude increases linearly, the reliability of the vehicle Sperling index experiences a quadratic or double-sloping decrease. Consequently, a maintenance threshold for OOR wheel amplitudes is given based on reliability considerations. Compared to Monte Carlo simulation, the proposed framework offers a computational efficiency improvement of at least one order of magnitude.</p
Generation of vibration load spectrum for fatigue analysis of equipment mounted on bogie frame of railway vehicle based on fatigue damage spectrum
No full textThe equipment mounted on the bogie frame of railway vehicles is subjected to non-stationary vibrations from the bogie frame. Currently, the vibration load spectrum for fatigue analysis of equipment is expressed with the power spectral density, which is generally obtained with the power values of measured vibrations or stationary Gaussian vibrations collected at the specific operating conditions. However, this does not have the equivalent damage potential as the non-stationary vibrations. Thus, a generation method of the vibration load spectrum is proposed based on the fatigue damage spectrum (FDS) to obtain the equivalent damage potential as the one from the non-stationary vibrations in this paper. That is, the FDS of non-stationary vibration is calculated with the time domain method, and the vibration load spectrum is generated in the frequency domain with this FDS. Then the method is verified by the measured vibration and dynamic strain of equipment. Finally, the vibration load spectrum of equipment mounted on the bogie frame is generated with the measured vibrations in a maintenance cycle and the fatigue analysis is performed. The results show that the generated vibration load spectrum can validly contain the high power in non-stationary vibrations and express the distribution of power over frequency, which gives much better estimates of the fatigue damage of equipment than other load spectra. The generated vibration load spectrum is suitable for quantifying the actual non-stationary vibrations and can be used for the anti-fatigue design of equipment
An efficient modelling approach to obtain dynamic properties of equipment coupled to the bogie of vehicle
No full textModelling the dynamic interaction between equipment and the bogie of a railway vehicle is crucial for the vibration and fatigue analysis of equipment. Current methods such as finite element and rigid-flexible coupling techniques are cumbersome. In this study, an efficient modelling approach is proposed to obtain the dynamic properties of coupled equipment. First, the vehicle and equipment are treated as independent modules, and further coupled using the frequency response function (FRF)-based substructuring method (FBSM). The FBSM is then developed from the finite element method to derive the FRF for the force to stress of equipment. Validation against experimental data and existing methods for a metro vehicle demonstrates the efficacy of our approach. The results indicate that the proposed approach models the vehicle and equipment as independent modules, eliminating the interdependent modeling steps of the previous approach and requiring less computation. The coupled small-mass equipment has a negligible influence on the dynamic properties of the vehicle bogie, but its dynamic properties are sensitive to vehicle and connection stiffness. Moreover, the vibration fatigue of equipment caused by the wheel/rail roughness can also be analyzed with the proposed approach
Fatigue analysis of coil springs in the primary suspension of a railway vehicle based on synthetic spectrum for time-varying vibration load
No full textThe fatigue life of coil springs is usually predicted with a stationary Gaussian vibration load and deterministic structural parameters. However, the obtained fatigue life is inconsistent with the observed fatigue life of fractured springs which varies within a wide range. The work aims to propose a method to predict the fatigue life of the coil spring by considering the time-varying vibration load, i.e., root mean square (rms) varies with time and the uncertainties of geometric parameters. First, a synthetic method for time-varying vibration loads is proposed. The time-varying load is decomposed into multiple stationary Gaussian short samples represented by their power spectral density (PSD). These PSDs are synthesized according to the distribution characteristics of spectral values, in which data that are non-Gaussian are processed with the Johnson system. Second, the influence of parameter uncertainties in the coil spring is studied by a Monte Carlo analysis of the stress frequency response function. Finally, the fatigue life is calculated and compared with the results predicted by using the measured stress. The results show that the synthetic spectrum has almost the same damage potential as the measured time-varying load. In comparison with results predicted from the measured stress, the synthetic spectrum gives much better estimates of the fatigue life of the coil spring than the average spectrum. Parameter uncertainties of coil springs significantly affect fatigue life and should be taken into account
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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