Browsing by Subject "Structural dynamics"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Dynamic response of structural elements undergoing moving loads and thermal strains using finite elements(2014-12) Paganelli, AnthonyMany structures undergo forced vibration due to moving loads: bridges, railway and subway tracks, aircraft carrier decks, etc. Many of these structures are also subjected to various types of thermal loading. Currently, there are limited or no analytical or experimental methods for analyzing the combined effects of the mechanically induced vibrations and thermal loads on complicated structures such as plates and curved beams with moving loads. Instead, it is more preferable to analyze such problems by numerically discretizing the spatial portion of the equations of motion using Finite Elements and the temporal portion with a numerical time stepping algorithm. The preferred time discretization method presented here is the GSSSS framework of algorithms in conjunction with the Finite Element method. This research will focus on: 1.) Developing a procedure for solving the dynamic response of structures undergoing forced vibration due to moving loads, 2.) Applying this procedure to curved beam structures, and 3.) Analyzing effects of the moving loads and thermal loads on the combined dynamic response of curved beams and flat plates. These developments provide a baseline for future research in the areas of combined transient thermo-mechanical problems using the GSSSS family of algorithms.Item Integrated dynamical models of down-the-hole percussive drilling(2014-07) Depouhon, Alexandre F.B.E.Due to the overall process complexity, studies about percussive drilling usually focus on a limited set of the (sub)processes underlying it, e.g., the hammer thermodynamics or the interaction between the bit and the rock. Following this paradigm, the assessment of the process performance is typically performed by considering a single percussive activation and a single interaction cycle between the bit and the rock, from arbitrary initial conditions.The need for an integrated approach to evaluate drilling performance, based on the dynamical interaction of the (sub)processes underlying drilling, is evident. Such an approach requires simplified models, however, as the computational cost associated with full scale models is simply unbearable. In this thesis, three dynamical integrated models are proposed and a preliminary analysis is conducted for a reference configuration and around it. The models couple three modules that represent: (i) the dynamics of the mechanical system, (ii) the interaction between the bit and the rock, and (iii) the activation of the mechanical system. For each module, simple representations are considered; of particular importance is the bit/rock interaction model which is a generalization to repeated interactions of experimental evidence observed for a single interaction.In the first model, the dynamics of a rigid bit is cast into a drifting oscillator and the activation modeled as a periodic impulsive force. The second and third models account for the dynamics of the piston and the activation results from the impact of the piston on the bit. They are respectively based on elastic and rigid representations of the two bodies. In the rigid model, analytical results of wave propagation in thin rods are used to represent the contact interaction between the piston and the bit. In the elastic model, wave propagation is resolved.Their preliminary analysis has revealed the occurrence of complex dynamical responses in the space of parameters. Expected trends are recovered around a reference configuration corresponding to a low-size hammer, with an increase of the rate of penetration with the feed force and the percussive frequency. An important sensitivity of the rate of penetration to the latter parameter is uncovered. Interestingly, our analyses show that when the activation period has the same order of magnitude as the timescale associated with the bit/rock interaction, a lower power consumption is observed, indicating a possible resonance phenomenon in the drilling system. Also, the predictions of the rigid model are shown to be in good agreement with the ones of the elastic model, in the explored range of parameters.Given the piecewise linear nature of the proposed models, dedicated numerical tools have been developed to conduct their analysis. As such, the thesis proposes a high-order time integration scheme for linear structural dynamics as well as a novel framework to evaluate the accuracy of such schemes, and a root-solving module to perform event-detection, for coupling with event-driven integration strategies. Specific to the framework is the account for both structural damping and external forcing in the evaluation of the scheme order of accuracy. Specific to the root-solving module is the forcing of event occurrence in the localization procedure.