Examinando por Autor "Mikkola, Aki"
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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 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 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 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.