DIMM-Artículos
URI permanente para esta colecciónhttps://hdl.handle.net/10953/243
Examinar
Envíos recientes
Ítem On the design of a scaled railroad vehicle for the validation of computational models(ELSEVIER, 2017) Fernández-Aceituno, Javier; Chamorro, Rosario; García-Vallejo, Daniel; Escalona, José LuisThis paper shows the procedure followed to design and manufacture a scaled railroad ve- hicle to be used in a scaled railroad track for the development and validation of compu- tational models. The purpose of this work is to address the background experienced by the authors from the ideal concept to the assembly one, and serve as a guideline for fu- ture railroad prototype designs. This specific vehicle, in which different inertial, guiding, recording and monitoring devices are installed, is mainly designed to be used in a 5-in. gauge railroad track for the validation of computational models and, as much as possible, designed with physical similarity with respect to a real railroad vehicle. The commitment between the imperative design requirements and the desired dynamic behavior is man- aged from the CAD design to its final assembly.Ítem An automatic procedure for calibrating the fracture parameters of fibre-reinforced concrete(ELSEVIER, 2025) Suárez-Guerra, Fernando; Donaire-Ávila, Jesús; Fernández-Aceituno, JavierIn this work a calibration procedure to obtain the material parameters that characterise the fracture behaviour of fibre-reinforced concrete (FRC) is presented. This procedure uses a proposed trilinear softening diagram recently implemented in a smeared crack model of the free finite element code OOFEM that allows reproducing the fracture behaviour of FRC and takes advantage of the optimisation package of SciPy, with both pieces of software being open-source and of free access for anyone interested in this field. This work presents the calibration procedure, which uses the Nelder–Mead algorithm to adjust the numerical result with the experimental diagram and discusses some key aspects, such as the number of reference points used in the calibration process or the weighting factors used with them, including the possibility of making some reference points more relevant than others in the calibration process. The influence of the mesh size and the element type used in the FEM model is also analysed. To evaluate the quality of the numerical approximation, a deviation factor is defined, which provides an scalar value that becomes lower as the numerical adjustment is closer to the experimental diagram in the reference points. The proposed procedure allows calibrating six parameters automatically with a meaningful time reduction and good accuracy. Using a higher number of reference points may lead to a better adjustment, although this study suggests that a good selection of the reference points is more effective than using a high number of reference points or using weighting factors to make some points more relevant than others. This procedure is finally validated by applying it with experimental results obtained with other types of FRC materials (different fibres and different fibre proportions) and specimen geometries.Ítem Wheel-rail contact force measurement using strain gauges and distance lasers on a scaled railway vehicle(ELSEVIER, 2020) Urda, Pedro; Muñoz-Moreno, Sergio; Fernández-Aceituno, Javier; Escalona, José LuisIn this paper, a 1 : 10 scaled dynamometric wheelset is presented. It has been equipped with two different technologies: strain gauges and distance lasers. The first one is based on the measurement of the wheel deformation with strain gauges and the second one on the measurement of the wheel web deflection with high precision distance lasers. The dynamometric wheelset has been carefully calibrated on a scaled calibration test bench. Several tests have been carried out on a 5-inch gauge scaled track to validate the dynamometric wheelset performance. The measured lateral and vertical forces of each experiment have been compared with an estimation drawn from a computational model of the scaled vehicle. A good accordance between the measurement and the model based estimation is achieved.Ítem Multibody model of railway vehicles with weakly coupled vertical and lateral dynamics(ELSEVIER, 2019) Muñoz-Moreno, Sergio; Fernández-Aceituno, Javier; Urda, Pedro; Escalona, José LuisIn the field of railroad dynamics, multibody models used for on-board state observation, parameter identification and track geometry measurement must ensure a high computational efficiency, particularly when real-time simulations are required. In this paper, a simplified model based on the assumption of weakly coupled lateral and vertical dynamics is proposed. Generalized forces included in the equations of motion are obtained using symbolic computations and the wheel-rail contact is modeled using knife-edge contact constraints and the concept of equivalent conicity. Resulting contact constraint equations can be solved analytically allowing the solution of ODE equations of motion in terms of independent coordinates. This general model considers arbitrary-geometry tracks including rail centerline irregularities. With the aim of showing the accuracy of the proposed model for the simulation of railways vehicle dynamics, a comparative study with a full 3D coupled dynamic model has been carried out for different vehicles and track geometries. The comparative study shows that the proposed simplified model in this work provides acceptable results for many applications. The model greatly improves the computational effort and it is applicable to real-life situations requiring a reduced set of parametersÍtem Models for dynamic analysis of backup ball bearings of an AMB-system(ELSEVIER, 2017) Halminen, Oskari; Fernández-Aceituno, Javier; Escalona, José Luis; Sopanen, Jussi; Mikkola, AkiTwo detailed models of backup bearing are introduced for dynamic analysis of the dropdown event of a rotor supported by an active magnetic bearing (AMB). The proposed two-dimensional models of the backup bearings are based on a multibody approach. All parts of the bearing are modeled as rigid bodies with geometrical surfaces and the bodies interact with each other through contact forces. The first model describes a backup bearing without a cage, and the second model describes a backup bearing with a cage. The introduced models, which incorporate a realistic elastic contact model, are compared with previously presented simplified models through parametric study. In order to ensure the durability of backup bearings in challenging applications where ball bearings with an oversized bore are necessary, analysis of the forces affecting the bearing’s cage and balls is required, and the models introduced in this work assist in this task as they enable optimal properties for the bearing’s cage and balls to be found.Ítem Multibody simulation of railway vehicles with contact lookup tables(ELSEVIER, 2019) Escalona, José Luis; Fernández-Aceituno, JavierThe use of contact lookup tables is widely used in multibody railway simulations to increase the computational efficiency. However, due to simplifying assumptions the use of contact lookup tables decreases the accuracy of the simulation results. This paper analyses the increase of computational efficiency and loss of accuracy for a particular multibody simulation. To this end the results based on contact lookup tables are compared with the results of the online solution of the wheel-rail contact constraints. The formulation used to compute the equations of motion of railway vehicles has the following features: (1) the equations of motion are obtained using a systematic procedure based on multibody dynamics, (2) generalized forces included in the equations of motion are obtained using symbolic computations when possible, (3) generalized coordinates are referred to a non-inertial track frame, (4) the equations of motion are obtained using a velocity transformation of the Newton–Euler equations of the vehicle bodies, which are assumed to be rigid and (5) wheel-rail tread contact and flange contact are treated with pre-calculated lookup tables which can take into account the track irregularities. The comparative study presented in this paper shows that this formulation can be used to simulate the dynamics of a railway vehicle in real-time.Ítem A touchdown bearing with surface waviness: Friction loss analysis(ELSEVIER, 2017) Halminen, Oskari; Fernández-Aceituno, Javier; Escalona, José Luis; Sopanen, Jussi; Mikkola, AkiThis paper presents a model for analysis of the chaotic turbulence in a touchdown bearing due to surface waviness. A multibody model of a bearing with surface waviness is presented. The model estimates the work done by the friction forces between the bearing components. Different waviness orders in the bearing inner and outer ring are examined by analyzing the friction losses in the touchdown bearing. The obtained results are compared with results reported in the literature. The proposed model supports selection of appropriate surface manufacturing accuracy for touchdown bearings to mitigate undesirable effects from surface waviness in a potential contact event.Ítem A nonlinear approach for modeling rail flexibility using the absolute nodal coordinate formulation(SPRINGER, 2016) Recuero, Antonio M.; Fernández-Aceituno, Javier; Escalona, José Luis; Shabana, Ahmed A.This paper describes a new nonlinear formulation based on the absolute nodal coordinate formulation (ANCF) for modeling the dynamic interaction between rigid wheels and flexible rails. The generalized forces and spin moments at the contact points are formulated in terms of the absolute coordinates and gradients of ANCF finite elements used to model the rail. To this end, a new procedure for formulating the generalized ANCF applied moment based on a continuum mechanics approach is introduced. The generalized moment is calculated using the spin tensor defined in terms of the gradients at the contact points, and therefore, the use of this approach does not require the use of angles. In order to have an accurate definition of the creepages, the location and velocity of the contact points are updated online using the rail deformations. An elastic contact formulation is used to define the contact forces that enter into the dynamic formulation of the system equations of motion. An elastic line approach is used to define the rail stress forces, and the relative slip between the rigid wheel and the flexible rail is iteratively updated using the deformation of the ANCF finite elements. The formulation proposed in this investigation is demonstrated using a five-body railroad vehicle negotiating flexible rails. In order to validate the ANCF rail model, the obtained results are compared with previously published results obtained using the floating frame of reference formulation that employs eigenmodes. The comparative study presented in this paper shows that there is, in general, a good agreement between the results obtained using the two different formulations.Ítem Application and Experimental Validation of a Multibody Model with Weakly Coupled Lateral and Vertical Dynamics to a Scaled Railway Vehicle(MDPI, 2020) Urda, Pedro; Muñoz-Moreno, Sergio; Fernández-Aceituno, Javier; Escalona, José LuisIn this paper, a multibody dynamic model of a railway vehicle that assumes that vertical and lateral dynamics are weakly coupled, has been experimentally validated using an instrumented scaled vehicle running on a 5-inch-wide experimental track. The proposed linearised model treats the vertical and lateral dynamics of the multibody system almost independently, being coupled exclusively by the suspension forces. Several experiments have been carried out at the scaled railroad facilities at the University of Seville in order to test and validate the simulation model under different working conditions. The scaled vehicle used in the experiments is a bogie instrumented with various sensors that register the accelerations and angular velocities of the vehicle, its forward velocity, its position along the track, and the wheel–rail contact forces in the front wheelset. The obtained results demonstrate how the proposed computational model correctly reproduces the dynamics of the real mechanical system in an efficient computational mannerÍtem Wheel–rail contact simulation with lookup tables and KEC profiles: a comparative study(SPRINGER, 2021) Escalona, José Luis; Yu, Xinxin; Fernández-Aceituno, JavierThis paper describes and compares the use and limitations of two constraint-based formulations for the wheel–rail contact simulation in multibody dynamics: (1) the use of contact lookup tables and (2) the Knife-edge Equivalent Contact constraint method (KECmethod). Both formulations are presented and an accurate procedure to interpolate within the data in the lookup table is also described. Since the wheel–rail constraint contact approach finds difficulties at simultaneous tread and flange contact scenarios, the lookup table method is implemented with a penetration-based elastic contact model for the flange, turning the method into a hybrid (constant in the tread and elastic in the flange) approach. To deal with the two-point contact scenario in the KEC-method, a regularisation of the tread– flange transition allows the use of the constraint approach in the tread and also in the flange. To show the applicability and limitations of both methods, they are studied and compared with special emphasis in the calculation of normal and tangential contact forces. Numerical results are based on the simulation of a two-wheeled bogie vehicle in different case studies that consider irregular tracks and two wheel–rail profiles combinations: profiles that do not show two-point wheel–rail contacts and profiles that do show two-point wheel–rail contacts. Although results show a good agreement between both approaches, the use of the KEC-method is more extensive since it allows to reproduce the wheel-climbing scenario that cannot be simulated with the lookup table method with the hybrid contact approach. It is concluded that simulations with this later method may not be on the safe side.Ítem Flow-induced vibrations of a hinged cavity at the rear of a blunt-based body subject to laminar flow(ELSEVIER, 2021) Jiménez-González, José Ignacio; García-Baena, Carlos; Fernández-Aceituno, Javier; Martínez-Bazán, CarlosWe perform numerical simulations to characterize the flow-induced vibrations (FIV) of a rear cavity with elastically hinged rigid plates, placed as a passive device at the base of a blunt body that is subject to a laminar flow of Reynolds number Re = 400 . The dynamic response and forcing of plates, wake features and force coefficients are investigated for the range of reduced velocity U ∗= [0 , 30] . Three different regimes of the rotational oscillations are identified. An initial branch of low oscillation amplitude is defined for U ∗< 2 . 5 , where the plates oscillate in counter-phase (varicose mode) with a frequency f p that corresponds to the harmonic of the wake vortex shedding frequency f p 2 f w , and is similar to the nat- ural frequency of the plates, f p f n . For intermediate values of U ∗, the plates oscillate in phase (sinuous mode) at their natural frequency, with respect to a closer averaged location of plates. Such synchronization regime amplifies the vibration magnitude and defines the upper branch in the amplitude response curve, whose maximum is attained at U ∗= 4 . 7 . Due to such enhanced vibration, the vortex shedding frequency is now locked-in at the natural frequency of plates, so that f p = f n = f w . Finally, for larger values of U ∗, a lower branch of moderate amplitude response is defined, which is characterized by the in-phase oscillation of plates, with respect to an more open average position, governed again by the shedding frequency, f p = f w > f n . Additionally, a multibody model has been developed to retrieve, from the plates rotational motion, the resultant forces and moments that produce the plates vibration. Such inverse dynamics model is formulated to allow its generalization for configurations of higher dynamical order, and validated against the results obtained from the numerical simulations. The analysis shows that the synchronization regime is mainly promoted by a reduced fluid damping and a forcing moment that acts in phase with the plates motion. The switch in such phase from 0 ◦to 180 ◦occurs after the lock-in, what attenuates the plates response at large U ∗. In general, the FIV of plates alters the vortex shedding and near wake pressure, especially during the synchronization regime, in- ducing an overall increase of the global force coefficients with respect to the static cavity.Ítem Analysis of two experimental setups to study mode II fracture on fibre-reinforced gypsum notched specimens(CSIC, 2023) Suárez-Guerra, Fernando; Fernández-Aceituno, Javier; Donaire-Ávila, JesúsThe main aim of this work is to study two relevant experimental setups designed for studying shear fracture and see if any of them allows studying the evolution of fracture under Mode II conditions, not only inducing a shear stress state at the onset of fracture. Two tests have been selected, a standardised test described by a Japanese standard, here referred to as the JSCE test, and the push-off test. These tests have been carried out on fibre-reinforced gypsum specimens with increasing proportions of polypropylene fibres and monitored by means of digital image correlation (DIC). The results show that fracture under Mode II conditions is relatively easy to induce with both tests, but once fracture begins, it is extremely difficult to induce a fracture process under Mode II. In general, Mode II has an important role at the onset on fracture, but Mode I predominates afterwards.Ítem Cumulative effects of cracking in monoblock multipurpose precast concrete sleepers on railway tracks(ELSEVIER, 2025) Donaire-Ávila, Jesús; Fernández-Aceituno, Javier; Suárez-Guerra, FernandoThis work addresses the phenomenon of cracking in multipurpose precast monoblock concrete sleepers by examining the entire process from fabrication to final installation on railway tracks. This includes stages such as manufacturing, stockpiling, track installation for rail neutralization, and eventually fastening the rails to the sleepers. A nonlinear numerical model, which is experimentally validated, is used to analyze this effect. Also, thermal and mechanical actions are considered at each stage of the process. Accordingly, different types of polymeric dowels and concrete aggregates—siliceous and carbonate—are evaluated to assess their impact on cracking. The results indicate that the thermal expansion capacity and elastic stiffness of the dowels, as well as the outdoor temperatures during fabrication, stockpiling, and installation, play critical roles in the cracking process. Sleepers made with carbonate aggregate, stiff-expansive dowels, fabricated in cold environments, and installed in hot conditions are particularly prone to severe cracking. Consequently, these conditions should be avoided to minimize cracking in multipurpose sleepers.Ítem Experimental study of the use of a transfer function to find rail corrugation from axle-box accelerations(ELSEVIER, 2025) Yu, Xinxin; Muñoz-Moreno, Sergio; Urda, Pedro; Fernández-Aceituno, Javier; Rodríguez-Gómez, Miguel; Escalona, José LuisThis investigation uses a scale vehicle-track experimental facility to study the calculation of rail corrugation using vertical accelerations measured in the axle-box of rail vehicles and a transfer function (TF). The rail corrugated profile is machined in the rail heads of the scale track following a periodic function with four harmonics. Experiments are performed with a scale bogie-like vehicle at different forward velocities in the range inspection velocities. Two simple analytical forms of the TF are studied: the kinematic TF, that assumes that the axle box follows the rail profile, and the TF of a 2-dof model of the vehicle-track system. For the vehicle response analysis, this work proposes to normalize the measured acceleration with the square of the forward velocity of the vehicle, that is assumed to be approximately constant. This normalized acceleration reduces the effect of the forward velocity on the TF. Experimental results show that the kinematic TF can be used to measure the track corrugation for moderate forward velocities providing reasonable but not accurate results. The limitation of the kinematic TF is mainly due to free flights and wheel rail curvature incompatibility. The measured axle-box accelerations may include frequency peaks that are not excitation frequencies and can distort the rail profile measurement. Results show that linear elastic models like the assumed 2-dof model do not explain the appearance of these non-excitation peaks.Ítem A touchdown bearing with surface waviness: A dynamic model using a multibody approach(SAGE, 2017) Halminen, Oskari; Fernández-Aceituno, Javier; Escalona, José Luis; Sopanen, Jussi; Mikkola, AkiThe amount of vibration induced by surface waviness in a touchdown bearing can be modelled with a multibody approach. This study develops a multibody model that accounts for surface waviness in races of touchdown bearings and employs the model to define the dissimilarities of the rotor and inner ring movements, and to perform inner ring velocity analysis in the frequency domain. Model results are compared with measured and simulated outcomes in the literature. Large movements are found in the orbits and velocities in the frequency domain due to surface waviness. Inner race eccentricity and ellipticity seem to be the cause of the most damaging surface waviness. In the frequency domain, all the significant peaks were noticed to be multiplications of rotor pendulum frequency, and the frequency of the inner ring was traceable in cases with waviness in the bearing. The model proposed in this study enables waviness to be taken into account in design of touchdown bearings.Ítem Influence of Rail Flexibility in a Wheel/rail Wear Prediction Model(SAGE, 2017) Fernández-Aceituno, Javier; Wang, Pu; Wang, Liang; Shabana, Ahmed A.The aim of this paper is to study the influence of rail flexibility when a wheel/rail wear prediction model that computes the material loss based on an energy approach is used. The wheel/rail wear model used in this investigation is a simplified combined wear hypothesis that is based on the frictional energy loss in the contact patch. In order to account for wear and its distribution in a profiled wheel surface, the contact forces, creepages and location of the wheel/rail contact points are first calculated using a fully nonlinear multibody system (MBS) and three-dimensional contact formulations that account for the rail flexibility. The contact forces, creepages and contact point locations are defined as nonlinear functions of the rail deformations. These nonlinear expressions are used in the wear calculations. The wear distribution is considered to be proportional to the normal force in the contact area. Numerical simulations are first performed in order to compare between the results obtained using the simplified wheel/rail wear model and the results obtained using Archard’s wear model with a focus on sliding when the track is modeled as a rigid body. This simplified wear model is then used in the simulation of the MBS vehicle model in the case of a flexible body track, in which the rails are modeled using the finite element floating frame of reference approach and modal reduction techniques. The effect of the rail deformation on the wear results are examined by comparing these results with those obtained using the rigid-body track model.Ítem Comparison of numerical and computational aspects between two constraint-based contact methods in the description of wheel/rail contacts(SPRINGER, 2022) Yu, Xinxin; Fernández-Aceituno, Javier; Kurvinen, Emil; Matikainen, Marko; Korkealaakso, Pasi; Rouvinen, Asko; Jiang, Dezhi; Escalona, José Luis; Mikkola, AkiThe numerical and computation aspects of the Knife-edge Equivalent Contact (KEC) constraint and lookup table (LUT) methods are compared in this paper. The LUT method implementation uses a penetration-based elastic contact model for the flange and a constraintbased formulation at the wheel tread. For the KEC method, where an infinitely narrow rail contacts an equivalent wheel, regularization of the tread-flange transition is adopted to simultaneously account for tread and flange contacts using constraints. A comparison between the two methods is carried out using well-known numerical integrators to show the applicability and limitations of both methods. Two fixed-step-size integrators, the explicit Runge–Kutta (RK4) and the predictor– corrector Adam–Bashforth–Moulton (ABM) methods, and two variable-step-size Matlab built-in function integrators, the explicit ode45 and implicit ode15s, were applied to get the numerical solutions to the dynamic problems and study the relative numerical performance of the two contact description methods. To complete the railway vehicle model, both contact methods were implemented for the multibody model of a benchmark railway vehicle (the Manchester wagon 1). Numerical results were obtained for different railway tracks with and without irregularities. Profiles of the S1002 wheel and LB-140-Area rail, which demonstrate the two-point contact phenomenon, were considered. Both methods were implemented in Matlab and validated against commercial simulation software. The kinematic results for both approaches show good agreement, but the KEC method was up to 20% more efficient than the LUT method regardless of integrator used.Ítem Friction Stir Welding Process Using a Manual Tool on Polylactic Acid Structures Manufactured by Additive Techniques(MDPI, 2025-07-22) Almazán, Miguel Ángel; Marín, Marta; Almazán-Lázaro, Juan Antonio; García-Domínguez, Amabel; Rubio, Eva MaríaThis study analyses the application of the Friction Stir Welding (FSW) process on polymeric materials manufactured by additive manufacturing (AM), specifically with polylactic acid (PLA). FSW is a solid-state welding process characterized by its low heat input and minimal distortion, which makes it ideal for the assembly of complex or large components made by additive manufacturing. To evaluate its effectiveness, a portable FSW device was developed for the purpose of joining PLA specimens made by AM using different filler densities (15% and 100%). Two tool geometries (a cylindrical and truncated cone) were utilized by varying the parameters of rotational speed, tilt angle, and feed rate. The results revealed two different process stages, transient and steady-state, and showed differences in weld quality depending on the material density, tool type, and material addition. The study confirms the viability of FSW for joining PLA parts made by AM and suggests potential applications in industries that require robust and precise joints in plastic parts, thereby helping hybrid manufacturing to progress.Ítem Machining characteristics based life cycle assessment in eco-benign turning of pure titanium alloy(2019-12) Gupta, Munish; Song, Qinghua; Liu, Zhanqiang; Pruncu, Catalin; Mia, Mozammel; Singh, Gurraj; Lozano, José Adolfo; Carou, Diego; Mashood Khan, Aqib Mashood; Jamil, Muhammad; Pimenov, Danil YuMinimum quantity lubrication (MQL) is considered as an eco-benign, greener, and socio-economic alternative to dry cutting. Nevertheless, its effectiveness is limited to mild cutting materials owing to less generation of heat during machining. In order to address this challenge regarding hard-to-cut materials, energy requirement, and material flow, Ranque-Hilsch Vortex Tube assisted Minimum Quantity Cutting Fluids (RHVT-MQCF) has been practiced in the turning of pure titanium and compared its effectiveness with conventional MQL cooling techniques. The turning experiments were performed on pure titanium alloy by varying the cutting speed (250–300 m/min), feed rate (0.05–0.13 mm/rev), and depth of cut (0.3–0.5 mm), respectively. In addition, a statistical modeling technique and desirability function approach was used to analyze and optimize the sustainable indicators for the machining process associated with the cutting force, power consumption, specific cutting energy, chips morphology, material removal rate, and surface quality (i.e. surface roughness). Regarding sustainability performance, Life Cycle Assessment (LCA) model was applied using Simapro 8.3 software connected to EPS 2000 and ReCiPe Endpoint v1.12 databases. Findings have depicted the high performance of RHVT-MQCF conditions regarding machining characteristics compared to MQL under same conditions. In-depth analysis has shown that RHVT-MQCF is a sustainable and useful alternative to the manufacturing sector.Ítem Numerical analysis of compliance and fatigue life of the CCC specimen(Elservier, 2023-01-23) Neto, Diogo Mariano; Antunes, Fernando Ventura; Sérgio, Edmundo; Branco, Ricardo; Camacho-Reyes, Alonso; Díaz-Garrido, Francisco Alberto; Gómez-Gonzales, Giancarlo Luis; Vasco, José ManuelThis study presents the numerical evaluation of the compliance in the CCC specimen aiming to assess the crack length inside the specimen. The numerical model considered the elastoplastic behaviour of the specimen, which is modelled using axisymmetric finite elements. The results shown that the propagation of the crack yields a nonlinear increase of the compliance. Nevertheless, variation of the compliance is very small for small values of crack radius. Considering a loading sequence composed by four load blocks of constant amplitude, the fatigue crack growth was predicted both using the Paris law and the numerical model. Both predictions agree but only the numerical simulation is able to capture the crack retardation between load blocks